What is the name of Cobra's high-speed sentry vehicle?

Cobra's high-speed sentry vehicle is the H.I.S.S. Tank.

H.I.S.S. is an acronym for High-Speed Sentry, the name of Cobra's heavily armed armored vehicle in the G.I. Joe toyline. The vehicle is designed as a fast, intimidating battlefield platform for Cobra troops and is one of the faction's signature machines.

The original H.I.S.S. Tank was introduced in 1983, making it one of the earliest major Cobra vehicles in the A Real American Hero toyline. It was commonly associated with Cobra's infantry forces and with Cobra Commander in media and packaging.

The other choices are separate vehicles. The Ferret is a Cobra all-terrain vehicle, the STUN is a Cobra attack vehicle, and the Rattler is a Cobra aircraft. The acronym is often written with periods as H.I.S.S., though “HISS Tank” is also widely used.