Gratuitous Space Battles (GSB) is a video game developed by the UK-based company Positech Games. At a high level, the title is a space battle simulation consisting of a number of engagements between two opposing fleets of ships. While sometimes assumed to be a real-time strategy (RTS) game based on screenshots, actual gameplay focuses on the setup prior to the battle, making it play more like a tower defense game.
From Official FAQ
The game is divided into a number of missions, which are big space battles fought in the name of something-or-other of no consequence. The aim is always the same: Destroy the enemies space fleet. Each mission has a different location, which may affect ship effectiveness due to local spatial anomalies and nebulas. You will fight against a fleet of fixed cost and number of pilots, and you will have to design a custom fleet for each battle, as both the situation, and the enemy fleet you face will be different for each mission
The game looks like an RTS in some screenshots, but is much more like a 'tower defense' game, in that you are not directly controlling your units, but placing them pre-battle and issuing orders. Imagine tower-defense, but with moving towers that you can design from scratch, in space, with cool laser effects. That is a fair approximation of Gratuitous Space Battles. You do not have control of individual ships during battle. The battle phase of the game is for visual feedback of how your fleet did. You can speed up and slow down and pause the battle to see what happens in some detail, and there are post-battle statistics showing who shot and killed who.