These boats have a battery capacity sufficient for a day's Fleet battle, but no more. They may be described as having great _strategic_ speed and capacity, but small tactical radius: that is, they can get to the place where they are wanted quickly, but are circumscribed in their capabilities of remaining submerged in that spot for long, or of moving fast submerged for more than one attack without rising to recharge their batteries. In submarine design as well as in that of surface ships, you can't have everything; each type is a compromise. At the other end of the scale we built the R boat. These were also "specialists," but of opposite qualities. Of 500 tons (submerged) they have a surface speed of about 8 knots, but a submerged speed of 14-1/2--a speed which will probably be slightly increased by alterations. These boats only joined up in the summer of 1918, and the enemy surrendered before they had really shown what they could do. A boat of this type (they are perfectly stream-lined, and, inside, they are all battery and torpedo tubes) can jog out to her assigned area at her leisure--it is no use sending her to cut off or meet a definitely reported enemy, as she wouldn't get there in time--and once in that area she can use her diving batteries for days without having to recharge them, should she be kept down by enemy hunters, and her high submerged speed and radius make her very dangerous to any target (U-boat or otherwise) which passes within periscope range of her. There remains the submarine monitor, which will be described in due course. I will interpolate here an account of a typical trial of a new boat, using an E boat of the early 1916 vintage as an illustration. II The boat I would use as an illustration was in 1915 very new indeed. She was just a standard E boat, with war-taught improvements and additions, and with a war-taught complement of officers and a half-taught complement of men. For a month the men had been given a queer but useful course of instruction by being taken by their First Lieutenant at "Diving Stations," in a disused shed in the building firm's premises. On the walls and floor names and rough sketches of most of the important valves and wheels of the boat herself had been chalked, and though the men laughed and swore at the make-believe, they had learnt a good deal of their drill and the probable sequence of diving orders, without the work of the builders of the E boat being interfered with. Except in the dinner hour, or during the infrequent holidays, no drill could be carried out aboard owing to the crowds of men working there. Overtime had been continuously worked, and nothing could be allowed to interfere with the firm's sacred "date"--the day on which the Admiralty had been promised delivery.