The balloon factories were now to supply the new demand of the balloon barrages that had been set up to protect such vulnerable points as the Firth of Forth and the Thames Estuary. The Thames balloon barrage, one of the units of which is seen below was worked from mobile barges. The men of the R.A.F. who manned the balloon sections had arduous work to do, for they had to face the bitter winds and rough water that winter brought to the North Sea area. Normally the crews did turns of 48 hours straight off, but in case it should be impossible to relieve them within that time the barrage barges were provisioned for six days. Each vessel carried a balloon crew of four men in addition to the crew of the barge. On each vessel were a balloon platform, winch, and a stack of hydrogen tubes. This was one of the first photographs taken of the new balloon barrage over the Thames Estuary which helped upset the nerves of the German airmen who were attempting to lay "murder mines" in the way of British and neutral shipping. In this case the anchorage of the balloon was a motor barge.