4000lb High Capacity "Cookie" bomb

The 4000lb high capacity bomb was the first of the large blast bombs to be designed and at the time was the largest ever to have been dropped by the British Air Force.  In September 1940 the Air Staff announced requirements for a new "mine-bomb" which would weigh 4000lb, the requirements were as follows...

• Ability of the Wellington to carry the bomb.

• Primarily for the attack of harbours, ships in shallow waters, canals and land targets such as oil plants.

• Capable of being released from 1,500 feet without breaking up.

• Instantaneous and delay fuzing.

• Bomb should also be able to be used as a magnetic mine, with a special magnetic fuzing system.

After discussion it was decided that the bomb was overly large for attacking surface ships and aircraft of the Fleet Air Arm could not carry such a large bomb so development of the 4000lb bomb and the magnetic mine were carried out separately. The filling of the bomb was also discussed and Amatol was decided, although RDX/TNT were preferable, large supplies of these explosives were doubtful at the time.

The primary concern was the installation of the bomb in the Wellington, this was taken up by Mr Barnes Wallis of Vickers Armstrong Ltd, who had been asked about the possibility of fitting a 4000lb bomb inside a Wellington in July 1940 and had suggested that the modifications could be completed in six weeks. In discussions in October 1940 the Air Staff decided that two obsolete Wellingtons should be allotted for modification to carry the bomb, after protest from Vickers this was changed to one aircraft that was currently under construction, a week later it was decided that all Wellingtons not to later in manufacture should be given the modifications.

The Air Staffs requirements for fuzing were complicated, for delay requirements, four axial exploder pockets were provided, these would be fitted with...

• A 0.5 seconds "Always" pistol.

• A 30 seconds delay pistol which would have to be designed.

• A 30 minute pistol which would have to be designed.

• A non disturbance or very long delay pistol.

These complicated requirements were dropped in later designs. The body was to be manufactured by suitable boiler making firms and an order for 50 was placed immediately. It was also decided to investigate the fitting of a ballistic tail as a parachute would put out the possibility of accurate bombing, both a ballistic tail and parachute were to be designed. By November the first bomb was ready with more nearing completion, this bomb was sent to Vickers for installation trails on the 24th of November 1940.

By December 2 bomb bodies had been sent to Woolwich for filling, six parachutes had been manufactured and the conversion of the Wellington by Vickers was nearing completion. First installation trails had not been entirely successful as no bomb trolley was capable of carrying such a bomb, the bombs were eventually attached to the release slip but it was found that the front could not be connected and so modifications were needed.

By mid February 5 bombs had been dropped, these were rather unsuccessful as some bombs oscillated badly and the parachute had caused the bomb the strike tail first and break up. Detonation in soft clay had given a crater similar to that of the 1,900lb GP bomb and so the bombs were unsuitable as a service weapon at this time. By the end of February there was great urgency for the bomb and Bomber Command was offered some experimental bombs for operational use and preliminary orders for 1,000 bombs.

Attempts to improve ballistic performance met with some success, a "nose spoiler" was fitted, this nose attachment formed the standard fitting for all HC bombs. By March trails with a drum tail were completed and the bombs dropped fell steadily, one was filled and detonated successfully, another inert filled fell on gravel and clay and did not break up meaning that the complications of a parachute were unnecessary (Air Staff later dropped the parachute requirement in August). In April the initial production order for 1000 bombs was followed by 360 bombs each month.

Up until May 1941 several 4000lb HC bombs had been used by Bomber Command and by August 1941 226 bombs had been dropped with no proved failures. The bombs were formally introduced into service in January 1942 as the Mark I.

There was several Marks of the bomb, the Mk II had some manufacturing changes and had three nose pistols instead of one, the Mk III was as the Mk II but without side exploder pockets. The Mk IV was as the Mk III but without the stiffening beam which had been added inside to strengthen the bomb for hoisting and suspension.

During a visit to England by General Arnold of the American Army, he was so impressed by the bomb that on his return to the U.S.A. he requested the American Ordnance Department to produced 4,000lb bombs of similar design and full details of the British bomb were made available, American produced bombs were known as the Mk V and VI.

Operational use

Over 93,000 4000lb high capacity bombs were released between 1941 and 1945 and it was estimated that these bombs were 1.4 times more effective as the same weight of medium bombs at causing structural damage. It is also interesting to note that a Wellington carrying a single 4,000lb HC carried over 2.5 times the amount of explosives as it would have if it carried 18 250lb or 9 500lb general purpose bombs.

4000lb High Capacity bomb statistics

Number of 4000lb High Capacity bombs released per year

Sources - AVIA 46 285, AVIA 46 163