Sticky Bomb - Development

Development

Since at least 1938, Jefferis had been toying with the idea of a demolition or anti-tank weapon that would be ideal for irregular warfare. It would work by having an explosive charge deform so that it has a substantial area of intimate contact with the surface of the target. Then, when detonated, the effect of the explosion would be focused on a small area and would rupture an armoured plate much thicker than would otherwise be the case. Sappers call such a device a "poultice" or "squash head" charge. Jefferis enlisted Drs Bauer and Schulman of the Colloid Science Department of Cambridge University, they had experimented with lengths of bicycle inner tube filled with plasticine to represent the explosive. These were fitted with wooden handles and dipped in rubber solution to make them sticky. In experiments, these prototypes proved difficult to aim and only by chance did any stick to the metal bins used to represent tanks.

With the end of the Battle of France and the evacuation of the British Expeditionary Force from the port of Dunkirk between 26 May and 4 June 1940, a German invasion of Great Britain seemed likely. However, the British Army was not well equipped to defend the country in such an event; in the weeks after the Dunkirk evacuation it could only field twenty-seven divisions. The Army was particularly short of anti-tank guns, 840 of which had been left behind in France and only 167 were available in Britain; ammunition was so scarce for the remaining guns that regulations forbade even a single round being used for training purposes.

Under the circumstances, Jefferis considered that his idea might have more general application for the British Army and the Home Guard. Jefferis was in charge of a department known as MIR(c), which had been created to develop and deliver weapons for use by guerilla and resistance groups in Occupied Europe. MIR(c) was now charged with the development of the Sticky Bomb.

The problem of designing a sticky bomb had been delegated to the enthusiastic genius of Robert Stuart Macrae. Clearly, some sort of flexible bag was required to contain an explosive gel so that it did not matter how the bomb landed on the target. However, a flexible bag is hard to throw and trials had not been at all satisfactory.

Discussions of the problem in Macrae's office were overheard by Gordon Norwood, a master printer who Macrae had recruited from his former magazine publishing employer, but he was not directly working on the weapon. Norwood suggested that what was needed was a frangible container and to the annoyance of the War Office store keeper he obtained a 150 W light bulb with which to demonstrate his point: a spherical glass flask inside a sock of woven wool is rigid when thrown, but on contact the glass breaks and the bomb deforms to the required shape. Experiments with glass flasks filled with cold porridge confirmed that this was the way to go. The grenade needed a delay for the thrower to get clear, so the woollen sock was covered in a sticky substance ensuring that the bomb stayed in place for a few seconds before detonating. Having covered the bomb in glue, a non-sticky handle was required; in the handle, a delay fuse ignited by releasing a sprung lever so that a five second time delay starts as the grenade leaves the thrower's hand (just like the levers found on a conventional Mills bomb type hand grenade).

Meanwhile, finding a suitable adhesive was a significant problem. After unsuccessful experiments with a variety of candidates, somebody suggested birdlime – a viscous sticky compound used since ancient times to trap birds by spreading it on tree branches and waiting for birds to get stuck. Birdlime performed better than anything previously tested, but it was still not good enough. Macrae's tin of birdlime was labelled with a large letter 'K' indicating that tin came from Stockport but with no more clues as the manufacturer. Macrae got on a train to Stockport and there found a helpful taxi driver who took him to Kay Brothers Ltd. The company's Chief Chemist was soon working on the problem of a suitable adhesive and within a matter of weeks the problem was solved to Macrae's satisfaction.

The filling for the bomb was developed by ICI. It was nitroglycerin-based with a variety of additives to make it more stable and viscous. The glass flask containing the main charge held about 1+1⁄₂ pounds (680 g) of this explosive that was described as having the consistency of Vaseline.

The adhesive surface was protected by a light metal case which was released by pulling a safety pin: the case fell away as two hemispheres connected by a sprung hinge. The inside of the case was fitted with a number of rubber spikes that kept it clear of the glued surface of the grenade. Early models also had a strip of adhesive tape round the neck of the casing.

Development continued, but there were problems with service regulations that were not written with such an unconventional weapon in mind. The sticky bomb was inevitably rather fragile and even a specially designed box could not fully meet the army's demanding requirements for withstanding rough handling without damage. It seemed there were problems at every turn. The Prime Minister, Winston Churchill, who was concerned with the state of the country's anti-tank defences, learnt about the grenade and urged its development. The Ordnance Board of the War Office did not approve the grenade to be used by the Army. However, Churchill ordered further tests to be conducted in July, and after personally viewing a demonstration of the grenade ordered that it immediately be put into production. His memo of October 1940 simply read "Sticky bomb. Make one million". A couple of days later, Anthony Eden, then Secretary of State for War, added a scribbled note to a cabinet minute that recorded the order to go ahead with the bomb:

Anti-Tank (& indeed anti-enemy generally) bombs for Home Defence are vitally urgent and should be available in very large quantities. I don't mind where they come from as long as we get them, home or abroad.

In spite of top level pressure, the arguments rumbled on. Trials were disappointing, it was not possible to get the bomb to adhere to any surface that was wet or covered with even the thinnest film of dried mud "a customary condition of tanks" as Major-General Ismay, on 27 June, could not resist pointing out.

Churchill was not amused:

General Ismay, I understand that the trials were not entirely successful and the bomb failed to stick on tanks which were covered in dust and mud. No doubt some more sticky mixture can be devised and Major Jefferis should persevere. Any chortling by officials who have been slothful in pushing this bomb, over the fact that at present it has not succeeded will be viewed with great disfavour by me.

Macrae, Ismay and Churchill all saw fit to record these arguments over the technical issue of stickiness. As Eden had pointed out, there was a lot at stake. The British infantry and Home Guard had little with which to put up a fight against tanks and to any who had witnessed trials of Molotov Cocktails and SIP grenades it was evident that they could do little to a modern tank other than to provide a blinding pall of smoke. What was needed was a hand weapon to deliver a coup de grâce by punching through the armoured plate. The sticky bomb could do the job and little else was available.

In his memoirs, Ismay recalled that he never solved the puzzle of how to convey his very genuine concerns of the time to the right people. A thrown sticky bomb simply would not reliably stick to a vertical surface. However, the bomb would stick if it was thrown onto the top of a tank where the plates were more or less horizontal – and thinner – but this reduced the throwing range to twenty yards at the most – getting that close would only be possible in an ambush or in street fighting.

Churchill considered any obstruction, however well-meaning, as singularly lacking in imagination. In the event of invasion, he foresaw a desperate fight to the last and after the war, he wrote about how he envisaged the use of the sticky bomb: "We had the picture in mind that devoted soldiers or civilians would run close up to the tank and even thrust the bomb upon it, though its explosion cost them their lives. There were undoubtedly many who would have done it ." He also later recorded how he intended to use the slogan: "You can always take one with you."

Arguments rumbled on and there were endless delays. Early versions of the sticky bomb were prone to leaks as well as breakage in transport. There were understandable concerns over the explosive charge: pure nitroglycerin is notoriously susceptible to the slightest knock, but the mixture developed by ICI proved to be very safe even if it should get into the hinges of the storage boxes. By December of 1940, fewer than 66,000 had been produced and the rate of production was disappointing at five to ten thousand per week. Further, it was suggested that the original order of one million be reduced to 200,000. Minor improvements to the design were made, of which the most significant was to replace the glass flask with plastic. Finally, after passing all the required tests, the sticky bomb – now the No 74 Grenade Mk II – was accepted by the Ordnance Board; it was put into full-scale production and it became a service issue.

On 14 May 1941, Lieutenant-General Sir Ian Jacob reflected:

The most extraordinary feature of the whole business, however, was the fact that the Secretary of State for War, in a Minute addressed to the Prime Minister on 25 November, 1940, said that the Director of Artillery and the Ordnance Board had only just been able to obtain from ICI the details of the explosive contained in the bomb. Seeing that the bomb was demonstrated in June 1940, this statement can hardly hold water. The War Office seems to be to blame in that, up to the end of April, 1941, no sticky bombs had been issued to any unit, nor had any dummies been provided for training. In view of our acute shortage of anti-tank weapons, the whole story is discreditable.

Between 1940 and 1943 approximately 2.5 million were produced.