Engineering Hitler's Downfall. Gwilym Roberts

      British and French troops enter Belgium to engage German forces.

      Churchill succeeds Chamberlain as British Prime Minister.

      26 May–3 June 338,000

      British, French, and Belgian troops evacuated from Dunkirk – all their equipment destroyed or abandoned.

      31 May British Cabinet decides to fight on, a decision supported by the British population.

      22 June Franco-German Armistice signed.

       Chapter 3

      LAND BATTLES LEAD TO DUNKIRK EVACUATION

      But Britain wins naval victory

      The disastrous first nine months of the war culminated in the heroic albeit desperate rescue of British troops from the beaches of Dunkirk at a time when early defeat stared Britain in the face. Within weeks of invading Denmark and Norway in April 1939, the Germans had invaded Holland, Belgium, and France with their new Blitzkrieg tactics – lightning-quick strikes with efficient communications so as to direct and coordinate its modern air force and mechanised army units. Attacking through Belgium and Holland, thus bypassing the Maginot Line, they achieved the overwhelming victory that led to the Dunkirk evacuation of more 300,000 British and French troops – and the French capitulation in June.

      This was in fact the second humiliating evacuation within weeks, the inglorious Norwegian Campaign (April–June 1940) having ended with our defeated troops being picked up from central Norway in early May. Gordon Corrigan wrote: ‘If the history faculties at universities were to run a module on how not to conduct a military campaign … then they need look no farther than the Norwegian campaign of 1940, for as complete and utter cock-ups it would be difficult to better.’

      During the retreat to Dunkirk the Royal Engineers (RE) demolished some 600 bridges, blew countless craters, and built improvised jetties on the beaches to facilitate the evacuation. The Light Aid Detachments of the Royal Army Ordnance Corps (the predecessor to the Royal Electrical and Mechanical Engineers (REME)) made valiant efforts to recover and repair damaged ordnance and vehicles, thereby enabling many items to reach the coast. Similarly, the Corps’ main workshop was successfully withdrawn to the coast by its commanding officer, Lieutenant John Nicholson RAOC, who was awarded the MC for achieving this with the minimum of losses. Sadly, they then all had to be destroyed or abandoned.

      Improvised jetty made by RE from abandoned lorries photographed by the Germans. IWM

      In the months prior to the retreat the British Army had built up its resources and equipment and generally prepared itself for the impending battle. Royal Signals, for instance, made use of the French civilian landline network with Army personnel working alongside local staff in their exchanges. Wireless telegraphy was regarded as a back-up to the landlines, the network being reinforced by the laying of additional dedicated lines where necessary.

      The hard lessons learned during the disastrous Norwegian and French campaigns made it immediately apparent that the procedures envisaged pre-war would have to be drastically rethought and that new techniques would need to be developed and applied. Principal among these operations were the importance of airpower, tactical mobility, close inter-service cooperation, rapid decision-making – and the need for modern equipment.

      Defeating the Magnetic Mine

      As Britain’s fate hung in the balance, a crucial engineering challenge was presented to Allied scientists: how to counter the menace of the mines sown on the bed of Britain’s shallow coastal waters by German ships and submarines or parachuted there by the Luftwaffe. So serious was the problem that the Port of London, then Britain’s busiest port, was nearly closed.

      These mines were detonated by the magnetic field of a ship passing over them, and it is notable that before those 800 ‘little ships’ sailed from Kent ports to rescue the troops stranded in Dunkirk, they had to be ‘wiped’ by teams from HMS Vernon to make them magnetically neutral.

      Sinkings off UK’s east coast September 1939–December 1940. Chatham Historic Dockyard

      HMS Belfast. Now moored near Tower Bridge. IWM

      The importance of the ensuing engineering feat was later expressed by one of its heroes, Commander Sir Charles Goodeve: ‘Although in the technical achievement the human effort was not in the same class as the radar or U-boat battle, it was the first technical battle in which we won a decisive victory over the enemy; but more important still, it was one which brought science fully into the war in the very early days.’

      The earliest casualty of the magnetic mines, the SS City of Paris, was damaged on 16 September while among naval casualties before the end of the year were the battleship HMS Nelson, which was put out of service for nearly a year; the newly commissioned cruiser HMS Belfast, which broke its back and took two years to be repaired; the destroyer HMS Blanche, which was sunk; Captain Lord Louis Mountbatten’s ship, the destroyer HMS Kelly, which had her stern blown off; and the minelayer HMS Adventure, which suffered serious damage.

      Caught unawares, and ignorant of how they operated, the Navy’s experts had to wait for mines to be dropped until they could be recovered and dismantled before they exploded. Two such mines were dropped by the Luftwaffe on the mud flats at Shoeburyness, Essex, in November 1939, and defused and dismantled by Lt Cdrs John Ouvry and Roger Lewis RN, and by CPOs Charles Baldwin and Archie Vearncombe of HMS Vernon. The pairs were awarded DSOs and DSMs respectively for their bravery.

      Thereafter, it was generally possible for the mines that could be found to be recovered and made safe, although sometimes things went wrong, with tragic results for those attempting to defuse them. The Germans also sometimes used delayed-action mines or booby-trapped the fuse mechanisms, adding to the hazards faced by the naval defusing teams. Among naval officers engaged in such work was Sub-Lieutenant (Sp) Peter Danckwerts RNVR, who was awarded the George Cross for his bravery. Detailed accounts of the mechanisms involved (which he described as ‘a miracle of ingenuity’) are contained in Danckwerts’ biography.

      Exploded view of magnetic mine fuse mechanism. Peter Varey

      Solutions also had to be found to protect ships from the mines that had been successfully dropped on the sea bed. A variety of counter-measures were investigated as a matter of urgency, but the two systems developed by Lieutenant Commander Charles Goodeve FRS RNVR proved most effective and were widely adopted. The first was to develop a system of detonating the mines which did not damage the vessels involved, and the second was to demagnetise ships.

      The former aim was achieved by the Double L Sweep, which involved two small wooden-hulled minesweepers towing a long loop-shaped buoyant electric cable between and behind them, through which strong electric DC currents were passed; the magnetic fields then induced in the sea were sufficient to detonate the mines.

      Danckwerts, Professor Peter GC MBE FRS (1916–84)

      The eldest son of Vice-Admiral Victor Danckwerts, who had seen action in HMS Kent during the 1914 Battle of the Falkland Islands and had been the Navy’s director of plans in 1940. He fell foul of Churchill when the latter was First Lord of the Admiralty and was removed from office, but later served in Washington before becoming second-in-command of the Eastern Fleet.