Guest article: Mayfly to Firefly – the Career of William Kilbourn

By David Andrews – member of the IMechE Engineering Heritage Committee

The Institution’s Top 5 Tanks video (see link below) highlighted the important role of William Kilbourn in developing the Sherman Firefly. With the help of the Institution’s archives and the Chertsey Museum more light can be shed on his long and interesting career.

In Normandy 75 years ago the Firefly (a Sherman tank fitted with the powerful 17 pounder gun) was one of the few capable of countering the heavy German tanks. On August 2nd, 1944 Winston Churchill gave a speech in parliament, it included the following:

As to the Sherman, I saw with my own eyes last week an example of the work of the 17-pounder. It was on the approaches to Caen. There was an expanse of large fields of waving corn out of which a grey stone village rose. Generals Montgomery and Dempsey brought me to this spot and invited me to count the broken-down Panther tanks which were littered about. I counted nine in the space of about 1,000 yards square. The generals then told me that all these nine had been shot with a 17-pounder from one single British Sherman tank from the side of the village wall. One cannot help being impressed by these things when one sees them with one’s own eyes.

Winston Churchill to Parliament, 2nd August 1944

The two score years and ten of an engineering career will span great changes. Older colleagues will retire, bloom and then fade away. Fresh faces will appear and in no time at all be married, have children and start to age themselves. The curfew tolls the knell of parting day and every year products will become more sophisticated, new technologies and processes will appear. The technology at the end of a career may bear little semblance to that at the beginning. Barnes Wallis started his career as an apprentice in the Thames Engineering Works in 1905 and retired from the British Aircraft Corporation in 1971. His career in aerospace started in 1913 when he moved to Vickers, working on the design of Airship No. 9 (the first British rigid design to fly) and culiminated in the research of hypersonic aircraft.

william kilbourn

Another engineer recruited by Vickers to work on Airship No. 9 was William George Kennings Kilbourn. Kilbourn had been born in 1892 in Leicester and had been an apprentice at the Adams Automobile Manufacturing Co in Bedford and the Edison & Swan Electric Co at Ponders End. Arriving at Vickers a year after Wallis, Kilbourn led a team of eight draughtsman working on the stabilising planes and the propeller swivelling gear. Airship No. 9 was the second rigid design that Vickers had built, the first, Mayfly, had never flown, a strong gust causing it to break its back while being removed from its shed. The remains of the Mayfly still lay in the airship shed for Wallis and Kilbourn to marvel at, to look round the decay of that colossal wreck like the ruined works of Ozymandias. Work on No. 9 was temporarily suspended in 1915 causing Wallis to join the Army and Kilbourn to be transferred to another part of Vickers where he spent the rest of the war designing gun mountings.

In 1922 Kilbourn was transferred to Vickers’ newly formed tank design section at Sheffield, starting an involvement with tanks that would last the rest of his career. Vickers wanted to break into a new market and their tanks were very successful in the inter-war period, being sold around the world. In 1929 the team was moved to Chertsey where Kilbourn spent the rest of his life. One pre-war project that Kilbourn was involved in was an twin-screw amphibious tank, one of which can be seen in the Tank Museum. With the war came a greater workload. Kilbourn’s work included designing a three man turret for the Valentine tank. The original turret only had space for a gunner and the tank commander, so the commander was also responsible for loading the gun, a distraction from his main duties. Kilbourn rearranged the turret to make space for a dedicated loader.

Kilbourn and the sherman

In 1942 Kilbourn (known as “K”) was transferred to the Directorate of Tank Design where he became responsible for the design of turrets, sights and gun mountings. The following year he received a ‘phone call from the Ministry:

“I’m going to ask you a question, K. But before doing so I must want you that the Americans say it is impossible, the British Army says it is impossible, and as a last resort I have come to you. The question is, can you by any chance put a 17 pounder gun in the American Sherman?”

Previously there had been plans to introduce new tanks, designed around this large gun, before D-Day. It was now apparent that they would not be ready and the only possible solution was to retro-fit the gun to the Sherman tank, which was available in large numbers.

Interviewed in 1979 Kilbourn related,

“I told London to ring me back in the morning when I would have the answer one way or the other. I brought all the drawings back here to the house, worked on it all night, and by modifying the breech of the gun, using parts from other gun mountings and without drastically altering the turret, I found I could get the gun in with one-eighth of an inch to spare! The next morning I gave London the answer and I was told to get a special design team together and work like stink to finish the job by Christmas. When it was all finished, I was sent down to a ministry establishment at Fort Halstead where I had to lay it all out in front of a dozen or so brass hats before it was finally agreed that it could be done.”

Kilbourn had to make various changes to fit the gun in the turret. The recoil system was altered to dramatically reduce the space needed when the gun was fired, the gun was rotated so the breech opened horizontally, the external shape of the barrel was changed where it was mounted to the turret and the tank’s radio was moved to a new bustle welded to the rear of the turret. The Firefly was available just in time for the Battle of Normandy and it was important in dealing with the latest German tanks, in terms of absolute firepower and in terms of psychology. The knowledge that they had the right tools for the job boosted the tank crews’ confidence.

Gun turret drawings, Courtesy of Chertsey Museum
kilbourn and later tank design

Kilbourn went on to work on the next generations of tanks. He was responsible for the turret and gun mounting of the Comet tank, followed by the Centurion. At the end of the war he was sent to Germany to report on German tank design, visiting several sites and interviewing his German opposite numbers. His career ended in the late 1950s working on the Chieftain tank. Kibourn also found time for several hobbies; he was an Associate of the Royal Photographic Society, solo tenor in a London church choir, a fuschia grower (his garden was famous in Chertsey) and he arranged a historical pageant, but above all that he was an engineer.

The Institutions Top 5 Tanks video presented by Rob Bell can be found on the Tank Museum YouTube channel: