Lt. is a written short form of lieutenant, a junior officer’s rank in the army, and also a rank in some navies, air forces and police forces. You write Lt. (or sometimes Lieut.); you do not say “L-T” in careful British speech — you read it as “lieutenant.” Americans sometimes do say “el-tee” in casual talk. The sound of the full word splits: in British English it is usually LEF-tenant; in American English, LOO-tenant. The abbreviation is the same on both sides of the water. A lieutenant is typically above a second lieutenant and below a captain in an army, though navies use the same word at a different height on the ladder, which is why a navy lieutenant is not “the same size” as an army one. You will also see Lt. Gov. for lieutenant governor — a deputy, “holding the place” of the governor.