In the Royal Navy, It is junior to commander and senior to the naval rank of lieutenant. Royal Navy ranks are matched up with Royal Air Force ranks. In this case the equivalent rank would be a squadron leader.
In the Royal Canadian Navy, the rank of lieutenant commander (LCdr) (French: capitaine de corvette or capc) is the naval rank equal to major in the army or air force. It is the first rank of senior officer.
This rank would be usual for a commander of a minor warship, or an executive officer in a larger ship.