Inflatable Enterprise

Star Trek: The Animated Series
Episode: TAS 22021 - Practical Joker, The

In 2270 (stardate 3183.3), when the Enterprise computer is infected by highly charged subatomic particles, it decides to pull a practical joke on three pursuing Romulans. Near the Neutral Zone, it releases an inflatable Enterprise, 20 times larger than the real Federation ship. The Romulans destroy the balloon, then chase the real Enterprise into an unknown energy field, thus infecting their own computers with the same "Practical Joker" subatomic particles.