Lieutenant (navy)
"First lieutenant" in naval usage
In minor war vessels, destroyers and frigates, the first lieutenant (either a lieutenant or lieutenant commander) is second in command, executive officer (XO) and head of the executive branch; in larger ships, where a commander of the warfare specialisation is appointed as the executive officer, a first lieutenant (normally a lieutenant commander) is appointed as his deputy. The post of first lieutenant in a shore establishment carries a similar responsibility to that of the first lieutenant of a capital ship.
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