To carry out such a system it was necessary to give each vessel a definite route which she should follow from her port of departure to her port of arrival; unless this course was adopted, successive ships would certainly be found to be following identical, or practically identical, routes, thereby greatly increasing the chance of attack.

In the early years of the war masters of ships were given approximate tracks, but when the unrestricted submarine campaign came into being it became necessary to give exact routes.
The necessary orders were issued by officers stationed at various ports at home and abroad who were designated Shipping Intelligence or Reporting Officers.

It was, of course, essential to preserve the secrecy of the general principles governing the issue of route orders and of the route orders themselves.

For this reason each master was only informed of the orders affecting his own ship, and was directed that such orders should on no account fall into the hands of the enemy.
The route orders were compiled on certain principles, of which a few may be mentioned: (a) Certain definite positions of latitude and longitude were given through which the ship was required to pass, and the orders were discussed with the master of each vessel in order to ensure that they were fully understood.
(b) Directions were given that certain localities in which submarines were known to operate, such as the approaches to the coast of the United Kingdom, were, if possible, to be crossed at night.

It was pointed out that when the speed of the ship did not admit of traversing the whole danger area at night, the portion involving the greatest danger (which was the inshore position) should, as a rule, be crossed during dark hours.
(c) Similarly the orders stated that ships should, as a rule, leave port so as to approach the dangerous area at dusk, and that they should make the coast at about daylight, and should avoid, as far as possible, the practice of making the land at points in general use in peace time.
(d) Orders were definite that ships were to zigzag both by day and at night in certain areas, and if kept waiting outside a port.
(e) Masters were cautioned to hug the coast, as far as navigational facilities admitted, when making coastal passages.
The orders (b), (c) and (d) were those in practice in the Grand Fleet when circumstances permitted during my term in that command.
A typical route order from New York to Liverpool might be as follows: "After passing Sandy Hook, hug the coast until dark, then make a good offing before daylight and steer to pass through the following positions, viz: Lat.