U. S. S. PENNSYLVANIA, Flagship
Cincpac File No.
Serial 01646
 PEARL HARBOR, T. H., October 14, 1941.
From: Commander-in-Chief, United States Pacific Fleet.
Subject: Security of Fleet at Base and in Operating Areas.
 (a) Pacific Fleet Confidential Letter No. 2CL-41.
 (b) Cincpac conf. ltr file A7-2 (13) Serial 01221 of 8 August 1941.
 (c) Pacific Fleet Conf. Memo. No. 1CM-41.
 (d) Pacific Fleet Conf. Memo. No. 2CM-41.
 (e) U. S. Fleet Letter No. 3L-40 (Revised).
 (f) U. S. Fleet Letter No. 19L-40.
 (g) Section 3, Chapter II, U.S.F. 10.
 (h) Chapter IV, U.S.F. 10.
 (A) Pearl Harbor Mooring and Berthing Plan showing Air Defense
 (B) Measures to be effective until further orders.

1. Reference (a) is revised herewith. References (b), (c) and (d), are canceled and superseded by this letter.

2. The security of the Fleet, operating and based in the Hawaiian Area, is predicated at present, on two assumptions:

(a) That no responsible foreign power will provoke war, under present existing conditions, by attack on the Fleet or Base, but that irresponsible and misguided nationals of such powers may attempt

 (1) sabotage, on ships based in Pearl Harbor, from small craft.
 (2) to block the entrance to Pearl Harbor by sinking an obstruction
 in the Channel.
 (3) to lay magnetic or other mines in the approaches to Pearl

(b) That a declaration of war may be preceded by;

 (1) a surprise attack on ships in Pearl Harbor,
 (2) a surprise submarine attack on ships in operating area,
 (3) a combination of these two.

3. The following security measures are prescribed herewith, effective in part in accordance with enclosure (B) or in their entirety as may later be directed by the Commander-in-Chief, U. S. Pacific Fleet, or the Senior Officer Present Afloat in the Hawaiian Area:


(1) Inshore Patrol (administered and furnished by Commandant Fourteenth Naval District).

(2) Boom Patrols.

(3) Harbor Patrols.


(1) Destroyer Offshore Patrol.


(a) The limits of this patrol shall be the navigable portion to seaward of a circle ten miles in radius from Pearl harbor entrance buoy number one Which is not patrolled by the Inshore Patrol.

(b) Three destroyers to search twelve hours prior to the sortie or entry of the Fleet or of a Task Force containing heavy ships. The Fleet or Task Force Commander concerned shall furnish this patrol and when a sortie and entry occur in succession the Commander entering shall furnish it.

(c) One destroyer (READY DUTY) to screen heavy ships departing or entering Pearl Harbor other than during a Fleet or Task Force sortie or entry. The Commandant Fourteenth Naval District will administer the Ready Duty Destroyer for this purpose and issue necessary orders when requested by forces afloat. Such Ready Duty Destroyer shall be on one hour's notice.

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(2) Air Patrols:

(a) Daily search of operating areas as directed, by Aircraft, Scouting


(b) An air patrol to cover entry or sortie of a Fleet or Task Force. It will search that part of a circle of a radius of thirty miles from the entrance channel buoys which is south of latitude 21-20' N. The Fleet or Task Force Commander concerned shall furnish this patrol, establishing it at least two hours prior to the sortie or entrance, and arranging for its discontinuance. When a sortie and entry occur in succession, the Commander entering shall supply this patrol.

(c) Air patrol during entry or departure of a heavy ship at times other than described in foregoing subparagraph. The ship concerned shall furnish the patrol mentioned therein.

(3) Daily sweep for magnetic and anchored mines by Fourteenth Naval District Forces. The swept channel for Fleet and Task Force sorties or entries is two thousand yards wide between Points "A" and "X" as defined in subparagraph (C) (3), below.


(1) Reference (h) will not be in effect in the Pacific Fleet during the present emergency.

(2) The Commandant Fourteenth Naval District controls the movements of ships within Pearl Harbor, the Entrance Channel, and the swept channel.

(3) Point "A" is midway between Pearl Harbor entrance channel buoys Nos. ONE and TWO; Point "A-1" is mid-channel on a line drawn 270 true from Buoy No. EIGHTEEN, Point "X" unless otherwise prescribed is three thousand yards bearing 153 true from Point "A".

(4) Zero hour is the time first ship passes Point "A-1" abeam for sortie, or Point "A", for entry, and will be set by despatch. Interval between ships will be as prescribed by Fleet or Task Force Commanders.

(5) Fleet and Task Force Commanders shall, for their respective forces:

(a) Arrange with Commandant Fourteenth Naval District for times of entry and departure, berthing and services.

(b) Prepare and issue sortie and entrance plans.

(c) Clear the Defensive Sea Area promptly after sortie.

(d) When a sortie and entry occur in succession, keep entry force well clear of Defensive Sea Area until sortie force is clear.

(e) Furnish own patrols except as modified by (B) (1) (b) and (B) (2) (b), above.

(6) Units departing or entering Pearl Harbor at times other than during a Fleet or Task Force sortie or entry, request authority and services as required, direct from Commandant Fourteenth Naval District.

(7) Heavy ships (including 7,500 ton light cruisers) maintain a minimum speed of 15 knots when within a radius of 15 miles from the entrance buoys to Pearl Harbor. During approach and entry, individual units govern movements to provide for minimum time in waters adjacent to the entrance.



(1)The Naval Operating Areas in Hawaiian Waters (U. S. C. & G. S. Chart No. 4102) are considered submarine waters. Observe requirements of reference (g).

(2) Ships, except submarines, shall anchor only in protected anchorages. Pearl Harbor is a protected anchorage. Hilo and Kahului are considered as such if boat patrols are maintained at the entrance and if ships are so moored as not be subject to torpedo fire from outside the harbor.

(3) Submarines may anchor in the following places: in Pearl Harbor, off Lahaina, inside or outside Kahului, off Kanai, and at Hilo. No boat patrols need be maintained.

(4) Submarines shall not operate submerged in the vicinity of surface ships except in accordance with prearranged plans for tactical exercises, for gunnery exercises, or for services to other types.

(5) Submarine operations, except (4) above, shall be confined ordinarily to Areas C-5, C-7, U-1, M-20, M-21 and M-24. Under special circumstances submarine squadrons may request additional areas from the officer responsible for assigning operating areas, who shall assign areas clear of the general area allocated to surface ships and shall notify all Fleet units in the Hawaiian area. While submarines are operating submerged in C-5 and C-7 they shall maintain a guard ship on the surface to warn approaching surface ships.

(6) Except as specifically directed for exercise purposes, all operations of submarines other than those covered in sub-paragraphs (4) and (5) above, shall be on the surface.

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(7) Commander Submarines, Scouting Force, shall ensure that commanders of surface and air task forces are furnished with detailed submarine schedules and all changes thereto. The latter shall ensure that units concerned, including air patrols, operating under their command are properly notified thereof.

(8) Ships proceeding independently across the operating areas at night shall follow neutral zones and area boundaries where practicable. The Task Force Commander in the vicinity shall be informed of: (a) the route to be followed using point numbers on the Operating Chart, (b) time of starting route, (c) the speed of advance. The Task Force Commander shall notify vessels of his force that may be concerned.


(1) When ships operate at sea from Pearl Harbor they shall be organized as a Task Force to which will be assigned destroyers and aircraft as necessary for screening. Each task force shall be organized offensively and defensively. These organizations shall be promulgated prior to leaving port and shall provide for the following:

(a) A destroyer attack unit to locate and attack hostile submarines.

(b) Anti-submarine screens for heavy ships in accordance with the number of destroyers available, priority in assignments being governed by the following:

Priority 1-BBs
 Priority 2-CVs
 Priority 3-CAs
 Priority 4-CLs

(c) A striking unit of cruisers, carrier (if operating) and destroyers, to co-operate with Patrol Wings and Army Air Units in destroying hostile carrier group.

(d) A concentration of own operating submarines preparatory to disposition as circumstances require.

(e) Inner air patrol for dispositions or formations, when in operating areas. Such screen shall be maintained by Task Groups, if the Task Force Commander so directs.

(f) Inner anti-submarine screens, insofar as practicable with assigned destroyers. Carriers operating alone utilize plane guards for screening when they are not employed in plane guarding.

(g) Maintenance of condition of readiness THREE on torpedo defense batteries and equivalent condition of readiness in destroyers. Supply ready ammunition and keep depth charges ready for use. Aircraft will not be armed unless especially directed.


(h) Maintenance of material condition XRAY, or equivalent in all ships.

(i) Steaming darkened at night in defensive disposition either as a Task Force or by Task Groups as practicable.

(j) Restricting use of radio to minimum required for carrying out operations.

(k) Maintenance of horizon and surface battle lookouts.

(l) Energizing degaussing coils whenever there is any possibility of the presence of magnet mines. Water of less than sixty fathoms shall be avoided if operations permit.

(2) Ships towing targets in operating areas at night will show appropriate running and towing lights, except when engaged in exercises the nature of which requires them to be darkened.


(1) Ships in port in the Hawaiian Area shall carry out applicable measures outlined in references (e) and (f).


(1) The principal Army anti-aircraft gun defense of Pearl Harbor consists of several three-inch mobile batteries which are to be located on the circumference of a circle of an approximate radius of five thousand yards with center in the middle of Ford Island. The Army, assisted by such units of the Marine Defense Battalions as may be available, will man these stations. Machine guns are located both inside and outside the circle of three-inch gun positions.

(2) In the event of a hostile air attack, any part of the Fleet in Pearl Harbor plus all Fleet aviation shore-based on Oahu, will augment the local air defense.

(3) Enclosure (A) defines the air defense sectors in Pearl Harbor and is the basis for the distribution of ships within the harbor for anti-aircraft fire. Hostile planes attacking in a sector shall be considered as the primary targets for ships in that sector. However, ships in other sectors may augment fire of any other sector at the discretion of the Sector Commander.

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(4) The Senior Officer Embarked in Pearl Harbor (exclusive of Commander-in-Chief, U. S. Pacific Fleet) shall ensure that ships are disposed at berths so that they may develop the maximum anti-aircraft gunfire in each sector commensurate with the total number of ships of all types in port. He is authorized to depart from the normal berthing plan for this purpose. Battleships, carriers, and cruisers shall normally be moored singly insofar as available berths permit.

(5) The Senior Officer Present in each sector prescribed in sub-paragraph (G) (3) above, is the Sector Commander, and responsible for the fire in his own sector.

(6) The Commandant Fourteenth Naval District is the Naval Base Defense Officer (N. B. D. O. ). As such he shall:

(a) Exercise with the Army joint supervisory control over the defense against air attack.

(b) Arrange with the Army to have their anti-aircraft guns emplaced.

(c) Exercise supervisory control over naval shore-based aircraft, arranging through Commander Patrol Wing TWO for coordination of the joint air effort between the Army and Navy.

(d) Coordinate Fleet anti-aircraft fire with the base defense by:

 (1) Advising the Senior Officer Embarked in Pearl Harbor (exclusive
 of the Commander-in-Chief, U. S. Pacific Fleet) what condition of
 readiness to maintain.
 (2) Holding necessary drills.
 (3) Giving alarms for: attack, blackout signal, all clear signal.
 (4) Informing the Task Force Commander at sea of the attack and the
 type of attacking aircraft.
 (5) Arranging communication plan.
 (6) Notifying all naval agencies of the air alarm signal prescribed.


(7) The following naval base defense conditions of readiness are prescribed:

Condition I-General Quarters in all ships. Condition of aircraft as
 prescribed by Naval Base Defense Officer.
 Condition II-One-half of anti-aircraft battery of all ships in each
 sector manned and ready. Condition of aircraft as prescribed by
 Naval Base Defense Officer.
 Condition III-Anti-aircraft battery (guns which bear in assigned
 sector) of at least one ship in each sector manned and ready.
 (Minimum of four guns required for each sector). Condition of
 aircraft as prescribed by Naval Base Defense Officer.

(8) Searchlights of ships shall not be used in event of a night attack.

(9) In event of an air attack, the following procedure shall be followed by the task forces:

(a) Senior Officer Embarked in Pearl Harbor.

(1) Execute an emergency sortie order which will accomplish (2), (3) and (4) below. (This order must be prepared and issued in advance).

(2) Direct destroyers to depart as soon as possible and report to operating task force commander.

(3) Prepare carrier with one division of plane guards for earliest practicable sortie.

(4) Prepare heavy ships and submarines for sortie.

(5) Keep Commander-in-Chief, Naval Base Defense Officer and Task Force Commander operating at sea, advised.

(b) Task Force Commander operating at sea.

(1) Despatch striking unit. (See (E) (1) (c), above.)

(2) Make appropriate defensive disposition of heavy ships and remaining surface forces at sea.

(3) Despatch destroyer attack unit if circumstances require. (May utilize unit of (E) (1) (a) for this if not needed for A/S purposes.)

(4) Direct commander of operating submarines to carry out action desired of him.

(5) Keep Commander-in-Chief, Naval Base Defense Officer and Senior Officer Embarked in Pearl Harbor informed and advised of any attacks or hostile planes sighted in the operating area.

(c) Naval Base Defense Officer.

(1) Give the alarm indicating attack is in progress or imminent. If not already blacked out, each unit shall execute blackout when the alarm is given.

(2) Inform the Task Force Commander at sea of the attack and the type of attacking aircraft.

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(3)Launch air search for enemy ships.

(4) Arm and prepare all bombing units available.


(1) In the event of a submarine attack in the operating area, the following general procedure will be followed:

Ship Attacked,

(a) Proceed in accordance with Article 509, FTP. 188. Originate a plain language despatch, urgent precedence, containing essential details addressed for action to the Task Force Commander in the operating area and for information to Commander-in-Chief, Commandant Fourteenth Naval District and S.O.P.A., Pearl Harbor. If the ship attacked is damaged, it will clear the immediate submarine danger area, at best remaining speed, then proceed toward Pearl Harbor using zigzag appropriate for speed in use.


Ships other than one attacked.

(b) Battleships. Zigzag at maximum speed. Launch aircraft armed for inner air patrol. Do not approach scene of attack closer than 50 miles during remainder of daylight period. Give own screening unit information to enable them to join quickly.

(c) Carriers. Same as for battleships, except place all aircraft in Condition ONE, armed. (At least one squadron with depth charges when they become available.) Aircraft for initial inner air patrol may be launched unarmed. Launch planes other than those for inner air patrol as ordered by Task Force Commander or as circumstances warrant.

(d)Cruisers. Same as for battleships, except, use one-half available aircraft (armed) for own inner air patrol. Send the second half to scene of attack (armed), to attack enemy submarine and to provide patrol for damaged ship if damaged ship has been unable to provide its own inner air patrol.

(e) Destroyers. Attack unit proceed at maximum speed to scene of attack. Take determined offensive action. Screening units join heavy ship units to which assigned. Destroyers in Pearl Harbor make immediate preparations for departure. Sortie on order of Senior Officer Present Afloat. Report to Task Force Commander when clear of Channel.

(f)Submarines. Surface if submerged. Remain in own assigned areas, zigzagging at best speed until directed otherwise.

(g) Minecraft. Augment screening units as directed by Task Force Commander.

(h) Base Force. If ship attacked is damaged, tugs in operating areas join her at best speed, prepared to tow, slipping targets as necessary. Report in code, positions of rafts abandoned. Tugs in Pearl Harbor prepare for departure. Sortie on order of Senior Officer Present Afloat. High speed towing vessels proceed at discretion, keeping 50 miles from scene of attack.

(i) Patrol Wings. Assume readiness for search and for offensive action. Carry out search as directed by Task Force Commander. Prepare to establish station patrol 220 mile radius from scene of attack at one hour before daylight of next succeeding daylight period.

(j) Shore-based Fleet Aircraft. Prepare to relieve planes in the air over the attack area, unless Pearl Harbor is also attacked, in which case the instructions issued by Naval Base Defense Officer have priority.

(k) Naval District. Clear Pearl Harbor Channel at once for either sortie or entry. Prepare to receive damaged ship(s) for repair.

(l) S. O. P. A., Pearl Harbor. Prepare destroyers in Pearl Harbor for sortie and direct the departure of units as requested by the Task Force Commander of units at sea. Control of departing units will pass to the Task Force Commander at sea as units clear the Pearl Harbor entrance buoys.

(m) Task Force Commander at Sea. Coordinate offensive and defensive measures. When immediate defensive measures have been accomplished; prescribe rendezvous and issue necessary instructions for concentrating and forming the Task Force.

(2) It must be remembered that a single attack may or may not indicate the presence of more submarines waiting to attack.

(3) It must be remembered too, that a single submarine attack may indicate the presence of a considerable surface force probably composed of fast ships

Page 480

accompanied by a carrier. The Task Force Commander must therefore assemble his Task Groups as quickly as the situation and daylight conditions warrant in order to be prepared to pursue or meet enemy ships that may be located by air search or other means.


4. Subordinate Commanders shall issue the necessary orders to make these measures effective.

Distribution: (5CM-41 )
 List II, Case 1: A, X.
 EN1, EN3, NA12, ND11AC, ND11-12-13-14, NY8-10
 (A1-Asiatic, A1-Atlantic).
Flag Secretary.

(At this point in Exhibit No. 4 there appears a map reflecting the Pearl Harbor Mooring and Berthing Plan showing Air Defense Sectors, Enclosure A., supra. This map will be found reproduced as Item No. 1, EXHIBITS-ILLUSTRATIONS, Hart Inquiry. These illustrations are bound together following the printed exhibits of the Hart Inquiry.) [Not currently available in the electronic version. LWJ]

 Enclosure (B)
(A) (1)
(A) (2)
 Boom-administered by Commandant Fourteenth Naval District with
 services furnished by Commander Battle Force from all ships present.
(A) (3)
 Harbor-administered by Commander Base Force with services furnished
 by Commander Battle Force from all ships present
(B) (1) (a) (b) (c)
 Furnished by Destroyers, Battle Force; Minecraft, Battle Force, and
 Minecraft, Base Force, and coordinated by Commander Destroyers,
 Battle Force.
(B) (2) (a) (b) (c)
(B) (3)
(C) (1) (2) (3) (4) (5) (a) (b) (c) (d) (e) (6) (7)
(D) (1) (2) (3) (4) (5) (6) (7) (8)
(E) (1) (a) (b) (c) (d)
 Assignments only shall be made. The Task Force Commander will hold
 one drill during each operating period, if employment permits, in
 the establishment of units prescribed.
(E) (1) (h) (i) (j) (k) (l)
(E) (2)
 The provisions of reference (e).
 Entire article, except sub-paragraph 6 (b), which will be as
 arranged by Naval Base Defense Officer with Commanding General,
 Hawaiian Department