A vast increase in British war production had been achieved in 1916 but the flow of equipment and ammunition caused transport problems in France, particularly on the (Nord) railways, which had become overloaded by the increase in the size of the BEF, the large number ammunition trains from the Channel ports to the Somme front and the need to move unprecedented numbers of casualties after 1 July. Congestion of the railways began to affect operations in July and rainy periods made delivery of ammunition from railheads to gun-positions much harder, when were being delivered even on "quiet" days. Shortages of heavy howitzer ammunition in mid-July were made worse in areas under German observation and harassing-fire, as more German artillery arrived on the Somme front.