cavalry

The military arm of service that fights while riding horses.

Two hundred heavily-armed cavalry rode behind the Audley standard, while close at their heels came the Duke of Lancaster with a glittering train, heralds tabarded with the royal arms riding three deep upon cream-colored chargers in front of him.

An individual unit of this arm of service.

The branch of the military transported by fast light vehicles, also known as mechanized cavalry.

A source of rescue, especially in an emergency.

call in the cavalry

"We landed in their killbox?" "We did. I am sor... No, belay that. Heads down! Cavalry incoming!"