A total of 212 Phoenix caissons requiring more than 600,000 tons of concrete and nearly 35,000 tons of steel were built on the banks of the Thames to prepare for the landing of June 1944. More than 20,000 workers took turns for 147 days to build these caissons under the supervision of engineer Jack Gibson. The first Phoenix caissons followed the landing armada across the English Channel behind tugs (four to eight depending on the size of the caissons) with only a few hours delay and began to be installed on June 7, 1944. Each of the following days, fifteen caissons crossed the English Channel. Of the 115 caissons weighing between 1,670 and 6,000 tons finally deposited on the Normandy coast in 1944, the remains of around twenty are still visible on the beach of Arromanches-les-Bains in the Calvados department.