The marines, in a word, do the sentry duty of the ship, but this does not prevent these sea soldiers and the sailors from getting on well together. Occasionally, a marine recruit, just assigned to a ship, will develop symptoms of a disease known as "duty struck," and blindly lay the foundation for years of unpopularity for himself by taking advantage of his authority to make it as warm as he can for the blue jackets, but such a recruit is quickly called to order by the older men of the guard. As a rule, the marines and blue jackets are on the most friendly terms, and there are few liberty parties of blue jackets bound for a good time ashore that are not accompanied by a favorite marine or two, invited along to help the sailormen dispose of their money, for, out of his $13 a month, the marine does not have a deal for shore use. The guard duty performed by marines on American ships is of an arduous and exacting kind. On some vessels, usually the smaller gunboats, the marine guard soldier is on post for two hours, and then gets only two hours off before buckling on his belt again, month in and month out. This sort of thing involves a breaking up of sleep that tells severely on marines serving on small ships, and it is for this reason that sea soldiers are so partial to flagships, and exhaust all the means in their power to be assigned to such large vessels of war. However, on every warship, no matter what its size, there is at least one first-rate billet for the private marine; that is the mail orderly's job. The mail orderly is the messenger between the ship and the shore, attends to all sorts of errands for officers and men, and is a general buyer of trinkets for all hands. A good deal of money passes through his hands, and his commissions are good, not to speak of the tips which are given to him for performing little diplomatic tasks ashore for the men forward. A marine mail orderly usually leaves the service at the expiration of a cruise with a snug sum tucked away. The first sergeant of a marine guard on a ship too small to rate one or more marine officers fills a responsible and exacting place, and is treated with great consideration by the officers, since, to all intents and purposes, he is an officer himself. He may go ashore when he chooses without putting his name down on the liberty list, and when he comes back to the ship from shore leave, he is not searched for liquor, an immunity which he enjoys in common only with the ship's chief master-at-arms. The first sergeant is responsible for the conduct of his men, and, if they do wrong, he is reproved much as if he were an officer. For the preservation of discipline, he is required to hold himself aloof from the members of his guard as much as possible, and he associates and frequently messes with the ship's chief petty officers.