Description: On D+1 the caissons, each with a 4 man crew, two sailors and an anti-aircraft gun emplacement, were towed to positions about a mile off-shore and handed over to a fleet of powerful harbour tugs which manoeuvred them into their final positions. The caissons' sea valves were opened until they settled at previously agreed depths. Each Mulberry was about a mile long and stood about 30 ft (9m) above sea level at low tide and 10 ft (3m) at high tide. The block-ships at Mulberry B were all in position by June 13th and formed two crescent shaped harbours which accommodated 75 Liberty ships and small craft.
The installation of the stores and LST piers proved to be more of a problem. The tows began to arrive at Mulberry B on D+4 and work continued throughout the night. Choppy seas made the manoeuvring of the bridging spans very difficult. By D+8 the stores pier and roadway amounting to 1.2k was in place and operational. The 2nd stores pier was operational by July 8. It was later discovered that the Beetle floats to support the roadway had been positioned in an alternate pattern rather than opposite each other as the design intended. This proved to be a costly error when consequential stability problems were experienced. The Luftwaffe attacked Mulberry B on July 15 but such were the defences that 9 of the 12 Messcherschmitts were shot down.
Mulberry A was in use for less than 10 days when, on June 19, it was severely damaged by the worst period of sustained severe weather for 40 years. Out of 31 caissons laid in position 21 were damaged beyond repair with broken backs and sides. Mulberry A was never used again and parts of it were scavenged to repair damage to Mulberry B. The Americans quickly reverted to the traditional methods of unloading from landing craft and DUKWs directly onto the beaches often coming in on one tide and leaving on the next. Such was their success that on occasions they exceeded the impressive performance achieved at Mulberry B.
Each day around 9000 tons were landed via Mulberry B until the end of August by which time Cherbourg port became available for use at least in part and, towards the end of the year, after the capture of Walcheren, the port of Antwerp. Mulberry B was in use for 5 months during which time over 2 million men, half a million vehicles and 4 million tons of supplies passed through the harbour. During this period several additional caissons where used to reinforce weak points in the breakwater.