AA. Defense Organization
Opinion expressed in action reports is widely divided as to whether suicide tactics present a new or the same AA. problem greatly accentuated. The tactic is relative new and currently produces about five times the success of previous forms of attack. The AA. problem is also new as long as the large proportions of the attacks is of a surprise nature and defense is restricted to a very short range problem. When search and lookout proficiency improves to the point that fire control contact is established either by radar or line-of-sight at the maximum range of the guns, the problem becomes essentially the same, complicated somewhat by the freedom of the attacking planes to take evasive action and the ship's necessity of producing an immediate kill.
The organization of the ship's AA. defense must be so set up as to permit it handling either the long range problem of shooting down the plane before it becomes dangerous, or engaging it destructively at a very short range. The primary requirement is simplicity. The organization must be so thoroughly understood by all hands that reactions become automatic. Fire control systems in all types of ships are presently designed to permit the maximum flexibility of control between various guns and fire control equipment. Utilization of all combinations of these systems in action is entirely impracticable. They are provided to take care of changing situations and casualties to existing systems, not as a test of the skill of fire control parties in handling complicated switching. Choice of the system which will give the highest probability of success must be made prior to action. Ships still report appreciation, after their first action, of the necessity for decentralized control.
Heavy AA. Gun Batteries
The most outstanding deficiency in Fleet AA. in suicide actions to date has been the performance of heavy AA. batteries. Previously (1 January to 1 July 1944) accounting for 39 percent of the kills credited to AA., the performance of 5-inch batteries against suicide planes has dropped to 18 percent. This is due to two factors namely:
Failure to engage at ranges in which the primary fire control system is most effective.
Failure to utilize most effective fire control methods available.
Establishing fire control contact at long range is a function of radar search. Utilization of the fire control systems and methods available is a function of the ship's internal organization.
Existing primary fire control systems in combatant vessels (Mark 37 or 33) are designed for dual purpose functions. Their efficiency in handling a critical AA. problem accordingly suffers. Unfortunately this deficiency does not become apparent as a result of training because the towed sleeve, with which the bulk of training is of necessity performed, lends itself well to the shortcomings of the system. Analysis of extensive data on Fleet shooting in action indicates that the average error of the shooting with primary system is on the order of 10 mils at ranges beyond 6,000 yards. Inside that range
errors rapidly increase, due to evasive action of the target, to 16 mils at 4,000 yards and 20 mils at 2,000 yards. Effective fire under such circumstances depends on:
Early engagement - The probability that a plane attacking in a typical situation will survive fire of three 5"/38 twins using Mark 32 fuzes is about 47 percent if fire is opened at 10,000 yards and continued into the minimum range of the battery. If opening fire is delayed to a range of 4,000 yards, there is a 70 percent probability that it will survive.
Large volume of fire - Where miss errors are probably large there is no substitute for volume of fire.
Use split battery fire - Again where the errors of each director are probably high, using the available battery split among the maximum number of directors that can bear pays dividends, especially when using VT fuzes.
Use short solutions; don't sit on a smooth solution. Since the inherent dispersion of the 5-inch batteries is low, a perfect solution with only a minor error in ballistic data (wind, density) will result in all bullets passing just out of reach of the target. Burst patterns of 20 mils, engendered by continuous small changes in the solution, are not excessive.
If caught in the primary system by a surprise attack, slew and shoot. Don't attempt a computer solution. Under such circumstances an estimate by eye should be dependable to 25 mils, and be within the errors of a snap solution.
Use the maximum percentage of VT fuzes practicable. Analyses of actions with early mods, with operability below 50 percent, show a three-to-one advantage over time fuzes. Latest mods should produce results of twice this figure. Some advantage unquestionably accrues from a small percentage of time fuzes. An initial timed burst at long range is an invaluable marker for other batteries. The psychological effect of an occasional timed burst on both the firing
ship and target should be considered. Fall of VT fuzed projectiles in enemy territory is now authorized. Fall of such ammunition among our own troops is to be avoided. Use of VT fuzes at short ranges is essential to eliminate possibilities of obscuring the target and of providing clues to the attacking plane for taking evasive action. At long ranges percentage should not drop below 75 percent; at short ranges 100 percent VT should be used.
Be prepared to use optical ranging when required. Several reports have indicated dependence on the rangefinder in suicide attacks because of multiplicity of planes or interference from a heavy burst pattern.
Virtually all combatant vessels and many auxiliaries are equipped to control their heavy AA. guns from some form of a lead-computing director (Marks 51, 52, 57, and 63) either as primary control in the case of the lesser ships, or as auxiliary directors in large combatant ships, with cross-connection to an adjacent 40mm. director. This type of director provides marked improvement in speed and flexibility of control of the heavy AA. batteries and suffers much less from evasive tactics of a close-in target than do the slower primary director systems. The accuracy and effectiveness of their control depends on skill of the director pointers, the accuracy of the range setting and the ballistics of the director.
The diagrams at the end of this chapter indicate errors to be expected as a result of improper ballistics and indicate range values within which the fire is effective for the 40mm. using 5-inch ballistics. The errors for the reverse process are almost identical, with the exception that the 5-inch fire then leads the target - a not undesirable situation. Analysis of previous experience with 40mm. mounts and the Mark 51 director, with estimated range setting, indicates errors on the order of 15-20 mils at ranges between 1,000 - 4,000 yards. With VT fuzes and such control the probability that a suicide plane brought under fire inside of 4,000 yards will survive is considerably less than one-third its survival probability if the primary director control system is used.
Utilization of auxiliary control systems for heavy AA. batteries as a solution of the short range problem has lagged in many ships because of the administrative problem involved in decentralization of control of these weapons. With the limited experience - of the crews and a large concentration of friendly ships and planes in the vicinity, commanding officers become loathe to place control of the 5-inch battery in stations other than the primary director system, where the most experienced personnel inevitably are located. The reduced efficiency of such a procedure is. unacceptable in face of the seriousness of the new attacks.
A definite organization is required that must vary considerably between ship types. It must be clear cut and the responsibilities of the various stations clearly outlined. The guiding principle should be that where possibility of surprise attack exists the heavy batteries should be distributed to sector control directors leaving the primary directors free for search and engagement of targets at long range. If a surprise attack occurs, there is no time for changing the fire control set-up, whereas if a target is contacted at long range sufficient time exists during solution of the problem to make the necessary decisions and shift of the 5-inch battery to primary.
The following excerpt from an action report describes a good example of proper organization of the heavy AA. battery:
USS Vincennes -- (Capt. A. D. Brown, C.O.)
"The events of the operation covered by this report served primarily to indicate further the effectiveness of the enemy's aircraft suicide dive attacks. The following paragraphs describe the AA. setup effectively used by this vessel during daylight after any approaching bogeys are suspected of having penetrated the cone of silence of the SK radar:
"The centerline 5-inch mounts are left switched to the forward and after Mark 37 directors and Mark 1 computers respectively, ready to take under fire in full automatic control the most dangerous targets, in accordance with the standard 5-inch doctrine. This setup rarely permits the centerline mounts to fire on an enemy plane not detected until in its dive, but does leave them available to take under fire more distant, approaching planes. These mounts use 50-50 VT and AAC projectiles."
(NOTE: A minimum of 75 percent VT is recommended for this battery. Retention of centerline mounts on the primary directors is justified where adequate coverage of the arc of the gun is not provided by the 40mm. or auxiliary directors.)
"The four waist mounts are switched to the four Mark 51 directors in their respective quadrants and follow the signal in indicating, while the 40mm. quads follow in automatic. The communications are divided likewise into quadrants, or sectors, as are the 20mm. circuits. These 5-inch mounts use 100 percent VT projectiles, and their standby condition is with a load in each tray ready to ram, and with the local firing circuit closed. The 40mm. twins are also in their indicated sector."
(NOTE: Control of 5-inch mounts from Mark 51 directors, either 40mm. or auxiliary 5-inch, has been authorized, and should be used.)
"The control of this setup is handled by the air defense forward and aft officers, who, receiving all available pertinent information from an AA. liaison officer in CIC, exercise direct control of their respective Mark 37 directors and advisory control of their respective sectors. Each sector, in turn, is controlled by an officer who exercises direct control of his respective Mark 51 director, with its associated 5-inch and 40mm mounts, and supervisory control of the 20mm. guns of his sector. When an enemy plane is visually observed (frequently already in its dive) in a sector, it is designated verbally to the director, which reports 'on target'; the sector control officer orders 'commence firing' to his sector: the 5-inch and 40mm. mounts commence at once, while the 20mm. guns commence only when the target is within their range. At the order 'cease firing' from the sector control officer, all guns comply and return to the ready position."
(NOTE: The director controlling the mounts also should have the authority and responsibility for opening fire when such situations require.)
"The setup described above is considered extremely effective against suicide diving planes. Since it has been in use on this vessel, only two planes have dived on vessels of the formation of which the Vincennes was a unit. However, both of these were taken under fire; one was probably damaged before it hit its target and the other was shot down in flames."
Automatic Weapon Battery
The outstanding feature in the engagement of suicide planes by automatic weapon batteries has been the character displayed by the men on the guns shooting it out. The ability of some planes to survive an incredible number of hits and still land on board has resulted in the conclusion that the plane has to be disintegrated to prevent its causing damage. While unquestionably a sure defense, only 20 percent of the planes deflected have actually been disintegrated or received severe structural damage to date. Of the successes due to automatic weapon fire, 63 percent has been credited to 40mm. The 20mm. guns have, however, done considerable execution and must be considered as an effective factor in the defense.
Shortcomings of the automatic weapons are typical of previous experience, namely, opening fire too early, insufficient lead, guns being drawn off the most threatening target, and poor fire discipline relative to the safety of adjacent ships.
Considerable improvement remains to be effected in decentralization of control, specific doctrine in range setting for 20mm. guns, responsibility of guns crews for lookout, and dissemination of information to guns. In respect to the last factor, many ships have existing loudspeaker announcing systems which can be used for rapid dissemination of target information. This is particularly true in the carriers, "whose bull horns reach virtually all parts of the topside.
Use of the Mark 14 gun sight has received some criticism in suicide actions. Intelligent use of the sight and expert range setting, however, still produce the greatest expectation of hits. A recent report from a training activity shows over a six-month period the sight producing about 150 percent of hits that were obtained by tracer control. For ships under direct attack by a diving plane rapid shift to a 400-yard setting is recommended for ease in getting on and control against a point blank target. For assisting ships range setters must be alert to provide a generous range setting to lead the target, compensating for its acceleration during the dive.
The difficulties that have been imposed on early radar detection of Jap suicide planes have been aptly summarized by CTF 38: --
Task Force 38 -- (Vice Adm. J. S. McCain, Commander)
"By combining the suicide dive with the lessons gained in past actions and a careful analysis of our defensive system, particularly our use of radar, the
Japs have developed the latest and most threatening problem that has yet confronted the U.S. Navy. The evasive-approach suicide attack shows not only the fanatical mind of the Jap, but what is far more dangerous, the application by the pilots and operations personnel of a complete understanding of radar and the complexities of air defense and air control. Specifically they have demonstrated an understanding of the following principles:
That a small group of planes attracts far less attention than a large group on a radar screen.
That an attack group approaching above or near returning strikes, which invariably straggle all over the skies in small groups, is very difficult to detect.
That if a bogie is at the same range, but 5 to 10 degrees off in bearing from a friendly, the average operator will have great difficulty in detecting the bogie, and when he checks each of the numerous straggling strike groups so carefully that he can tell a bogie in their midst, the radar is able to do very little searching.
That a bogie at the same range and bearing but vastly different altitude from a friendly appears as a friendly.
That multiplicity of small targets is one of the weaknesses of any radar system or, for that matter, of any defense system.
That altitude has always been a weak point in radar defense, and that although the SM can hold a target and give accurate altitude on it, a number of small targets changing altitude and course are extremely difficult to track and obtain continuous correct altitude.
That we search with one type of radar set and, finding a target, try to coach the Fighter Director Set (SM) onto the target for evaluation, altitude, and tracking if necessary.
That by approaching very high in fast power glide from long range, the radars are given a particularly difficult problem, both by lack of altitude estimates on the SK-SC and by being continuously in the null area of some sets.
That the use by the enemy of dull black planes for these attacks makes visual sighting most difficult.
"The use by enemy of an IFF that looks like Mark III Code 1, 2, or 3 is definitely established. The possibility of the enemy using planes with the outstanding silhouette characteristics of the F6F should not be overlooked."
The problem of search for fighter direction and tactical purposes differs from that of search for AA. requirements. The former requires early detection at the maximum possible range. The AA. problem, however, commences at 15 mile At night, with relatively few planes in the air and reduced fighter direction demands, considerable success has been had in coordinating the two problems. In suicide actions, however, the concentration of friendly planes, the non-cooperative tactics of the Japs, the frequent proximity to land and the demands
of fighter direction result in CIC providing little assistance in establishing fire control contact in a large majority of the cases. Although no single typical case can be presented the experience of TG 77.2 well illustrates the situation:--
"At 1702 the ship went to General Quarters upon receipt of report of bogie, bearing 270 degrees (T), distance 45 miles, closing the formation. The bogie was tracked in from 75 miles to 45 miles, where it was lost in geographic returns from the area. The Army CAP was vectored to intercept and later reported shooting down one twin-engined plane.
"At 1715 visual reports were received of enemy planes overhead, in the sun.
"At 1716 an enemy plane, believed to have been a twin-engined Lily or Frances, was sighted by this ship's lookouts, coming out of the sun at about 8,000 feet, parallel to the course of the formation. The plane was taken under fire by 40mm. batteries from U.S.S. NEW MEXICO. Less than 5 seconds later the plane had peeled off into a dive on opposite course coming in over the port bow of the Ommaney Bay in a dive of 45 degrees. The plane struck the ship on the starboard side of the flight deck, just aft of the island structure."
(NOTE:-At 220 knots this raid would be over the formation at 1715.)
Extensive comment has been made on the deficiencies of existing equipment for short range and high angle search. Many specific recommendations have also been received for better utilization of existing equipment, principally in the employment of fire control radar to augment the existing search coverage. An elaborate AA. coordination plan was proposed by Essex (CV-9) aimed at better dissemination of information for the AA. problem, coordination of search by fire control radars and centralized control or coordination of AA. fire. Task Groups 58.3 and 58.4 have proposed trial of the plan but report of its application has not been received to date. CTG 58.4 statement of the plan is quoted below;
Task Group 58.1 -- (Rear Adm. R. W. Radford, Commander)
The purpose of the AA. Coordination Plan is to assist in the detection of close-in bogeys, shifting of contacts from search to fire control radars, and the early engagement of enemy planes by concentrated gunfire while guarding against further undetected attacks.
"The plan provides for:
Sector assignments for search and for distribution AA. fire in event of multiple targets.
A close-in radar search using fire control radars.
A voice radio circuit for the dissemination and exchange of AA. gunnery information.
An AA. coordinator stationed in the flagship.
This plan will be placed in effect upon sorties from Ulithi, and will be operative when Condition One is set in AA. batteries.
AA. Coordination Plan.
Heavy ships are assigned sectors of 120°; 60° on each side of the bearing line from the disposition center.
The ship in the center of the disposition is assigned a 360° sector, but will concentrate on most likely bearing of approach.
Destroyers are assigned sectors of 150°; 75° on each side of the bearing line from the disposition center.
Fire Control Radar Search
Ships may search at discretion, covering their own sectors as thoroughly as practicable and will track contacts in their assigned sector.
Search with AA. fire control radars will be conducted using 20° antennae elevation with Lobing "On." Main battery radars may be used for low altitude search.
When searching, the sector should be covered at approximately one minute intervals.
Contacts will be reported on the AA. coordination circuit, giving call of ship reporting and the bearing, range, and altitude. All bearings will be true bearings. Amplifying reports will be made when further information is available.
The AA. coordination circuit will be established, and will be cleared of all other traffic during Condition I.
Standard voice procedure and TBS calls will be used.
The purpose of this circuit is to provide a channel for the INTERCHANGE of AA. gunnery information between ships of the task group.
The group AA. coordinator is in no sense a control officer.
His purpose is only to provide information and to coordinate effort, aiming toward early engagement of enemy planes.
Sector assignments in no way restrict the bearings on which a ship may fire. Sectors are NOT "sectors of responsibility". However in case of multiple targets, the primary target will be those approaching in the assigned sector.
A close liaison must be maintained between CIC and AA. control stations of individual ships in order to utilize all available information.
It is hoped that this plan will increase the effectiveness of AA. gunfire by providing close coordination, and early engagement of enemy planes. The additional information available should facilitate "picking up" targets at longer ranges. No restrictions are placed on freedom of action by individual ships in repelling air attacks. Since this plan is in an experimental stage, criticisms and comments are desired."
The concept of the first two functions is excellent. It is essential that information flow both within the ship and between ships of the task force as to location or probable location of targets within a radius of 15 miles. Establishment of a search plan for fire control radars is properly a function of the Task Group Commander and should be varied to meet the existing situation. No search plan with a fire control director, however, should interfere with an individual ship's establishing fire control contact by either radar or line of sight on an enemy plane. Coordinated control of AA. fire of a task group should be either permissive or restrictive. Detailed control and target designation in the fast-moving AA. problem in general would be impossible.
40 MM FIRE WITH 5" 38 CAL. GUN ORDERS IS NOT EFFECTIVE UNTIL PRESENT RANGE DROPS TO 2500 YARDS
40 MM. FIRE WITH 5" 38 CAL. GUN ORDERS IS EFFECTIVE AT HIGH ANGLE DIVE AT RANGES OUT TO 5000 YARDS
40 MM. FIRE WITH 5" 38 CAL GUN ORDERS ON CROSSING RUNS IS NEVER EFFECTIVE UNLESS TARGET RANGE FALLS BELOW 2000 YARDS
40 MM. FIRE WITH 5" 38 CAL. GUN ORDERS IS NOT EFFECTIVE UNTIL PRESENT RANGE DROPS TO 3500 YARDS
Ommaney Bay (CVE-79) about four minutes after being hit by suicide plane in Sulu Sea. She sank about an hour later. West Virginia (BB-48) in foreground.
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