harassing the workers. Machinery such as excavators, pile drivers, cranes, floodlighting, and concrete pumps (which were still a relatively new technology in the 1940s) was temperamental, and in the case of steam-driven equipment, very noisy. Bunkers had to be able to accommodate more than just U-boats; space had to be found for offices, medical facilities, communications, lavatories, generators, ventilators, anti-aircraft guns, accommodation for key personnel such as crewmen, workshops, water purification plants, electrical equipment, and radio testing facilities. Storage space for spares, explosives, ammunition, and oil was also required. Types of bunker Four types of bunker were constructed: Covered lock These were bunkers built over an existing lock to give a U-boat some protection while it was at its most vulnerable – i.e. when the lock was emptying or filling. They were usually constructed with new locks alongside an existing structure. Construction bunker Used for building new boats Fitting-out bunkers After launch, many U-boats were fitted-out under their protection Shelter for operational boats and repair bunkers This was the most numerous type. There were two types that were built either on dry land or over the water. The former meant that U-boats had to be moved on ramps; the latter enabled the boats to come and go at will. Pumping the water out enabled dry dock repairs to be carried out. Some bunkers were large enough to allow the removal of periscopes and aerials. There is no truth in the rumour of an underground bunker on Fuerteventura in the Canary Islands. This story was gleaned from a similar situation in Le Havre in France when captured U-boat men were interrogated by the British. Locations Pens were constructed in the northern coastal ports of the Reich and in many occupied countries. Germany Pens protecting construction of the Type XXI submarine were located in Hamburg (Blohm & Voss), Bremen (AG Weser), and Danzig (F. Schichau). Bremen The "Hornisse" bunker was not started until 1944 in Bremen; it was never completed. "Valentin" was the largest bunker in Germany. Begun in 1943, it was built to be a manufacturing facility, where Type XXI submarines were to be constructed. It too was never completed. Post-war, it was briefly used as a test site for British and American bombs (most of the damage done to the bunker was inflicted at this time) before becoming a storage facility for the German Navy. The labour to construct it