The arming of the merchant ships was the first defensive measure to be adopted; the second, the gathering of merchantmen into escorted groups known as convoys. Now a convoy has before it several definite problems. If it was to make the most of its chances of getting through the German ambush, it must act as a well coördinated naval unit, obeying orders, answering signals, and performing designated evolutions in the manner of a battleship squadron. For instance, convoys follow certain zigzag plans, prepared in advance by naval experts. Frequently these schemes are changed at sea. Now if all the vessels change from plan X to plan Y simultaneously, all will go well, but if some delay, there is certain to be a most dangerous confusion, perhaps a collision. It is no easy task to keep twenty or so boats zigzagging in convoy formation, and travelling in a general direction eastward at the same time. Merchant captains have had to accustom themselves to these strict orders, no easy task for some old-fashioned masters; merchant crews have had to be educated to the discipline and method of naval crews. Moreover, there have been occasional foreign vessels to deal with, and the problem presented by a foreign personnel. In order, therefore, to assure that communication between the guide ship of the convoy and its attendant vessels which is, in the true sense of an abused word, vital to the success of the expedition, the Navy placed one of its keenest signalmen on the vessels which required one. He was there to give and to send signals, by flag, by international flag code, by "blinker" and by semaphore. The wireless was used as little as possible between the various vessels of the merchant fleet, indeed, practically not at all.