He studied at the University of London; but he abandoned this for a two-year certificate course with the Officer Training Corps when the First World War broke out in 1914.

LoLode produced a wide range of trailers based on Clarke's design for a low-slung chassis and four close-coupled wheels with a stable suspension system.

Macrae explained that he had been contacted by Major Millis Jefferis of the War Office, who had read a brief article in Armchair Science that described very powerful magnets.

[18][19] Macrae visited Clarke at home and after "sweeping a number of children out of the living room",[4] he laid out his rough drawings and the two men soon agreed to cooperate on the design of a new weapon.

[4] Small horseshoe magnets were fixed in the grooves and with a filling of porridge in place of high explosive, the first prototypes were created.

Clarke's son John later recalled:[24] I remember going with my father in the motor boat and we trundled up and down the Ouse at different speeds with this underwater device, which nobody could see because it was under the water.

So that was yet another test that my father had to undergo and it was all extremely interesting and exciting.The next step was to design a delay mechanism so that when a limpet mine had been put in place, the bomber would have plenty of time to get away before the explosion.

As Professor Lindemann told you in the strictest confidence, experiments are in hand on somewhat similar lines and as soon as results are available, so that we can tell whether your ideas can be applied, you will be informed.

A great deal depends upon the type of soil and the conditions in which the machine will have to be used, but, in certain circumstances, which may well occur, the method you propose might be applicable.

Drawing on his experiences of trench warfare in the First World War and his particular expertise in tunnelling and explosives, he drew up a proposal for an armoured trench-forming machine.

[29] His trench-forming machine would drive through the earth advancing 2,000 yards in a single night, men and tanks following in its wake in the relative safety of the trench it had formed.

[35] The mine was being manufactured by the Special Operations Executive (SOE) at their Technical Research and Development Station at Aston House near Stevenage, Hertfordshire,[35] and there were some problems with the original model to be ironed out.

[40] Having resigned from his job at the Admiralty, Clarke joined the Army and was taken on by Wood to work at Aston House, where he was put in charge of training SOE saboteurs.

[43] This was placed over the spigot and when the propelling charge was fired, the projectile would fly off; this sudden acceleration also armed the contact detonator.

[44] Simple, quiet, and easily portable, the spigot gun was an ideal weapon for the saboteur and it was thought very suitable for jungle warfare.

[44][41] The weapon was fired by pulling on a lanyard, by a trip wire as part of a booby trap, or by a pencil detonator delay mechanism.

[41] One account of its use describes a trip wire for a locomotive; placed up high it was likely to be missed by track walkers looking for bombs on the railway line.

[42][49] In December 1940, Clarke was promoted to Captain (acting Major) and appointed as the commandant of Brichendonbury Manor, SOE's Station XVII.

[51] In an example later recalled by his son, he took his team out one dark night and using scaling ladders they got past the guards and into Luton Power Station.

[56] After reconnoitring their target, the Pessac transformer station, the agents were put off by the difficulty of getting past the guards, the nine-foot-high wall and a high-tension wire.

Instead the raiders lay low for a month and then made their attack with special equipment to climb over the walls and open the main gate.

The nearby U-boat docks were put out of action for months, 250 people were arrested, the Pessac area was fined one million French Francs and 12 German guards were shot.

[57] Operation Anthropoid was the code name for the assassination attempt on SS-Obergruppenführer and General der Polizei Reinhard Heydrich, the Nazi Germany acting Reichsprotektor of the Protectorate of Bohemia and Moravia.

[59] At Aston House, Clarke and Wood trained Czechoslovak soldiers Jozef Gabčík and Jan Kubiš to throw the bombs into a slow-moving vehicle by using an old Austin rolled down a ramp.

[59] Clarke was also involved in the training of agents who went on to attack ships of the French Fleet at Oran in Algeria in November 1942,[62] and in 1943 the agents of Operation Gunnerside which destroyed the heavy water plant at Rjukan, Vemork, in Norway[62] – an operation later evaluated by SOE as the most successful act of sabotage in all of World War II.

[64] The exact circumstances of his transfer are unclear; it seem that his unconventional training methods – breaking into RAF and transformer stations – had made him unpopular.

[65] The altimeter switch was extensively used by the OSS, who distributed it to Chinese forces, especially those in Chungking,[66] where it was used to assassinate Dai Li, the widely hated head of the Kuomintang (KMT) secret police.

[69] MD1 had prospered as the war progressed and the department had little difficulty getting hold of two Churchill tanks and the large amount of steelwork required.

[68] On the first live test the rockets were so powerful that they nearly pulled the tank along with the flying ramp, as a result of which the driver was "not in good shape", but Clarke persisted with the trial and the viability of the design was confirmed.

[75] Without deploying its projected ramp, the Great Eastern could be used to bridge gaps of up to 40 feet (12 m) such as an anti-tank ditch with a vertical retaining wall.