From the introduction to The Fourth Edition;
Experienced Signal Close Action players will want to know what's new in Fourth Edition. Well, the concept of the Ability Chart is still fundamental to the rules - particularly as it cuts down on the need for excessive record keeping. This time, however, there are more dice and they play critical roles. In the past if you had a 'bad throw' then all your actions were affected. With Fourth Edition the dice are colour coded with one being common to all. The score of this common dice is added to the dice relating to the various actions.
Other new innovations include the division of a player's part of a turn into two segments and reloading, so that the time scale of actions are more realistic. The firing rules are not changed noticeably but there are new separate charts for firing at Unrated vessels.
The main rule book takes you through setting up a game, all you need to know e.g. Vessel Statistics, Sequence of Play, and descriptions of the main actions of the game.
The Appendices has advanced game options such as Tactical Initiative, Strategic Initiative, Outlying Patrol Vessels and Boatwork. A glossary of terms used during the period is also provided with the beginner in mind.
Any base size can be used as distance is measured from mast to mast. So no problem if you've already got ships based.