Four ships of the Royal Canadian Navy, including two guided missile destroyers, are being retired as the service modernizes its fleet.

The Department of National Defense identified the vessels as the navy's Protecteur and Preserver, auxiliary oil replenishment ships, and the destroyers Iroquois and Algonquin.

"The retirement of these vessels has been anticipated for some time, and is a step towards the introduction of new ships and capabilities set to be delivered through the National Shipbuilding Procurement Strategy, as well as recognition of the RCN's commitment to the responsible use of public funds while maintaining Canada's naval readiness," the department said.

Canada's National Shipbuilding Procurement Strategy, or NSPS, is a $33.3 billion program for the recapitalization of the federal surface fleet and includes the modernization of 12 Halifax-class frigates, procurement of three new classes of ships -- including joint support Ships, Arctic/offshore patrol ships and surface combatants -- as well as the integration of new maritime aircraft into fleet service.

HMCS Iroquois, the first-of-class guided missile destroyer, will retire in January. It was originally scheduled for retirement in 2011, the department said. HMCS Algonquin, the fourth Iroquois-class destroyer, will retire in "the near future." The ship has been docked since 2013 since sustaining extreme damage in a 2013 collision with the oil tanker Protecteur during an exercise.

"Considering the relatively short service life remaining for HMCS Algonquin, which was scheduled to be retired in early 2019, and its current state of repair, the cost to re-instate this ship to full operational capability no longer represents a responsible use of public funds." the department said.

The two oil auxiliary ships are being retired soon and ahead of when they were originally scheduled.