After the destruction of the first Death Star it was clear the Lambda-class T-4a shuttle wasn't going to suit all the needs of the Empire. The Empire were in need of a shuttle that could operate both as a large scale troop transport, heavy cargo carrier or a VIP command station for extended periods of time.
Two SFS-500 sublight ion engines and a hyperdrive, give the Command Shuttle the ability to get anywhere it needs to quickly and efficiently. With configuration options for 4 crew and 5 VIP guests or 4 crew and 40 troops, the shuttle quickly became a widely used craft, on and off the battlefield.
Although not specifically a battleship, the shuttle was still able to defend itself if needed with it's two Taim and Bak KX5 double blaster canons as well as four ArMek R-Z0 heavy blaster canons.
Because of it's large engine size and power, the shuttle was also used in the transport of AT-AT's from Imperial Star Destroyers to the planet of Hoth in Empire Strikes Back.