The yacht and boat building and design firm, William Weatherhead and Sons, had been building fishing boats from their yard in Cockenzie since 1880. In June 1940, along with a number of other firms, an order was placed with Weatherhead's for a construction of motor launches.

This work posed a number of problems for the firm, mainly due to the much larger size of a motor launch (M.L.) than a fishing boat; the keel of an M.L. was two and a half times longer than that of an average fishing boat. It was also discovered that the firm's shed at Cockenzie was too low and, rather than raise the roof, it was decided to excavate the floor, creating the extra space needed. The first ship completed was M.L.168 and, being the first, it was decided that it should be given a traditional launch. However, further problems were created when orders were placed for more motor launches. The yard was too small in which to build more than one vessel at a time and therefore another shed was built on vacant land alongside, the firm carrying out the work itself as outside contractors could not give a completion date.

The increased workload for the yard meant that Weatherhead's had to take on many more workers, but with vastly increased shipbuilding during wartime, such skilled tradesmen were all in employment. As a result, the only solution was provided by the Ministry of Labour's local exchange which supplied joiners, although there was initially some confusion until the new tradesmen learned to convert "sharp end" and "blunt end" to "bow" and "stem" and all the other associated naval terms.

Weatherhead's was also given contracts for the construction of landing craft which required changes in building technique since they were made of steel plate. For a firm which had predominantly worked with wood, this was quite a change, but the challenge was successfully met, with one landing craft being built in 15 weeks.

The motor launches and landing craft were mainly prefabricated, the parts being supplied from Cobham in Surrey under the control of Fairmile Marine Company. The firm also built cabin cruisers for the War Office, these being used to transport army personnel to islands round Britain.

The great expansion of Weatherhead's during the war years saw the number of employees rise from 9 men to, at their peak, over 100 working on military contracts.

The workers were particularly pleased to receive a visit from some M.L. officers who had been in combat with German U-boats, the tales of their experience making the ship builders feel that they were really doing something for the war effort.

The Cockenzie fishing industry helped the war effort in other ways too. The local fishing fleet was commandeered by the Royal Navy and was used to patrol the Firth of Forth. These vessels became known as 'Harry Tate's Navy'.