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d20 Modern System Reference Document



The rules for starship combat are based on the rules for character combat. Like character-scale combat, starship battles unfold on a square grid, with each starship occupying one or more squares on the grid. As with character-scale combat, starship battles play out in rounds.

The starship combat system presented here strikes a balance between realism and ease of play. The system can be made more realistic by adapting bits and pieces of the vehicle movement and combat rules to the 500-feet-per-square starship scale.

These basic starship combat rules also assume that all starships involved in the battle are crewed by nonheroic characters. What happens when heroes take the controls is discussed later.


Every starship has a type and a subtype. A starship’s type represents its relative mass and determines its fighting space (how many 500-foot squares it occupies) on the battle grid. There are five types of starships: ultralight, light, mediumweight, heavy, and superheavy.

A starship’s subtype identifies the ship’s basic purpose or configuration. Starship subtypes include the following: fighter, corvette, destroyer, strike cruiser, battleship, and freighter.


Each square in starship scale measures 500 feet along a side (instead of 5 feet, as in character-scale combat). All starships, regardless of size, have a square fighting space. Some starships occupy a single 500-foot square, while others have a larger fighting space, as noted below.

An ultralight starship can be up to 250 feet long. It occupies a 250-foot-by-250-foot fighting space, and up to four ultralight starships can occupy a single 500-foot square.

A light starship measures 251–500 feet in length. It has a 500-foot-by-500-foot fighting space and occupies a single 500-foot square.

A mediumweight starship measures 501–1,000 feet in length. It occupies a 1,000-foot-by-1,000-foot fighting space (4 500-foot squares).

A heavy starship measures 1,001–1,500 feet long. It has a 1,500-foot-by-1,500-foot fighting space (9 500-foot squares).

A superheavy starship is 1,501 feet long or longer. The smallest superheavy starships (measuring 1,501–2,000 feet long) have a 2,000-foot-by-2,000-foot fighting space (16 500-foot squares), although larger fighting spaces are possible.

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