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        AND REFER TO NO.

Bureau of Ships

Washington, D.C.
3 June 1941



Subject:  Aircraft Carriers - Venting of Explosions in hangars.

     1.   The phenomena connected with explosions of heavy charges in enclosed spaces are exceedingly complex and the laws governing them are not well established. The hypothesis that the energy of a high-order explosion can be vented by an opening or orifice of moderate proportions has been frequently advanced and was strongly held by the British Navy which issued instructions in their Damage Control Handbook that certain hatches were to be left open or un-dogged for the venting of shell and bomb bursts or underwater explosions. Experiments and war experience have, according to a summary of action damage during the first year of the war recently received, shown that blast damage is not in most cases, appreciably reduced by the fitting of vent plates or by venting through hatches and watertightness is now regarded, at least up to probable flooding levels, as of greater importance.

     2.   This conclusion confirms the opinion held by Rear Admiral Stocker, and confirmed by subsequent experiments certainly as regards the space in which explosion actually occurs in which the generation of pressure occurs with lightning rapidity. In adjacent spaces where the time-pressure gradient is less, gases may have time to escape through openings and so relieve pressure on the structure. This has been indicated by tests conducted during the past two years at the Naval Proving Ground.

     3.   In the case of bomb-burst in the hangar of 103 (HMS Illustrious was repaired in the United States at Norfolk Navy Yard following bombing by German dive bombers in January of 1941< under "Work request 103"), while the final effects nave been viewed, a full report of the damage is not yet available, and all the circumstances of the explosion are not known. The following appear to be established:-

(a) The after elevator was down.
(b) The forward elevator was up.
(c) The 60-lb. doors at both ends were open.



     (d)   These doors were roughly of one-third the total area of the end bulkheads, i.e., the cross section of the hangar.

     (e)   At least one roller (fire) curtain was down.

     (e)   The heavy A.P. bomb burst above the hangar deck almost on the centerline 30 feet from the open after elevator well and 375 feet from the open splinter doors, but closed forward elevator well.
           (NOTE:  Elevator wells are 22' x 45' immediately forward and abaft transverse armored bulkheads at the ends of the hangar).

     (g)  A pressure wave ran forward in the hangar like a sound wave in an organ pipe augmented perhaps by small initial resistance of roller curtains until it was obstructed by the heavy end bulkheads which carried in one-third the total width on each side to the open doorway to the elevator. Due to this obstruction, including the elevator in the up position, the wave was reflected and built up sufficient dynamic pressure, (1) to dish the 40-lb. armored deck down about a foot over nearly the full width the hangar, and (2) to 1 buckle the forward elevator platform up some three feet.

     (h)  The pressure wave from the explosion would be expected also to travel aft. The fact that the after elevator well was open may nave permitted the pressure wave to escape without damaging the heavy structure in the vicinity, but the pressure wave may well have caused further damage to the elevator platform itself and surrounding light structure which had been previously damaged by two bomb hits. The platform was a mass of wreckage lying in the after well. In other words, the damage from the first two hits in the after elevator well obscured any results of the hangar hit in that location.

     (i)  There was a great deal of damage done purely by blast in compartments as far as three decks below the explosion.

     (j)  Whatever the cause for the fact that there was no blast damage visible around the after elevator well, it is certain that the fact that the gases could "vent" out this opening did not prevent serious blast damage elsewhere and probably had no effect whatever in reducing such blast damage.


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     (k)  The roller curtains did heavy damage to planes and personell as they were driven forward through the hangar.

      4.  Any practicable venting along the side would probably not have reduced or materially changed the damage at the forward end of the hangar. The LEXINGTON and SARATOGA hangars are likely under similar circumstances to show the same phenomenon.

     5.  The hangars of the RANGER, YORKTOWN, ENTERPRISE and WASP have large side areas which can be closed only by light roller curtains. The ratio of such openings to total side area however, may not be of itself sufficient to alter the blast effect unless the bomb hit occurred just in way of a pair of very large openings. The surrounding structure is, however, very light and will suffer heavy fragment and blast damage. A reliable prediction of the effect of a heavy bomb hit in these hangars is not possible on information now available.

     6.  An investigation of the effects of high order explosions in air-filled spaces has been planned. The details are yet to be developed. It is intended to use the degree of confinement as one of the variables.


E. L. Cochrane


Copy to:

National Archives & Records Administration, College Park
Record Group 19, "Item S-24 Records Relating to Foreign Ships & Ordnance"

Transcribed by RESEARCHER @ LARGE. Formatting & Comments Copyright R@L.

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