The Deployable Practice Target can be described as an inflatable starship.
The device is made of a triple monolayer of materials starting with an organic polymer designed to keep gasses inside, followed by a psudofluid sealant layer, and finally a metallic film which reflects sensors and small metallic patches that reflect light to create the illusion of on-ship lighting. Since it is deployed in space, it only needs 27 cubic meters of compressed dry nitrogen to inflate fully. Deflated, the Practice target is about the size of a desk and can easily be deployed from the proton torpedo tubes once primed.
Direidi natives, Thedd and Orvy, niece and friend of Ross Flyter, were accidentally beamed aboard the USS Enterprise (NCC-1701) when they were snooping around inside the Smith's escape pod. After escaping notice and managing to enter the cargo decks, the duo found a Deployable Practice Target [Prototype, Klingon], and beamed it and themselves to the planet surface. Tedd and Orvy twisted a lever, causing the it to inflate. The Klingon battlecruiser-shaped `balloon' drifted away, and soon deflated, draping itself over the top of the Direidi Great Hall. (TOS novel: How Much for Just the Planet?)