"First lieutenant" in naval use The first lieutenant in the Royal Navy and other Commonwealth navies, is a post or appointment, rather than a rank. Historically the lieutenants in a ship were ranked in accordance with seniority, with the most senior being termed the "first lieutenant" and acting as the second-in-command. Although lieutenants are no longer numbered by seniority, the post of "first lieutenant" remains. 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 specialization 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 the first lieutenant of a capital ship.
"First lieutenant" in naval use The first lieutenant in the Royal Navy and other Commonwealth navies is a post or appointment, rather than a rank Historically the lieutenants in a ship were ranked in accordance with seniority with the most senior being termed the "first lieutenant" and acting as the second-in-command. Although lieutenants are no longer numbered by seniority, the post of "first lieutenant" remains. 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 specialization 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 the first lieutenant of a capital ship.