The first AW101 Merlin MK4 rotary-wing aircraft delivered to the U.K. Royal Navy by Leonardo-Finmeccanica has taken its maiden flight.

Leonardo says the aircraft completed its first successful flight test at the end of October. The milestone comes as the company upgrades 25 Royal Navy Merlin MK3 aircraft as part of the force's Merlin Life Sustainment Program. Deliveries are expected to begin in 2017, and continue until 2020.

"This is a great day and a most significant achievement in the Merlin Life Sustainment Program. The conversion of the Mk3/3a Merlin to Mk4/4a has been a real success story so far against demanding timelines and this first flight is excellent news for our Royal Navy 'Junglie' customers," Royal Navy Captain Kieran O'Brien said in a press release.

The AgustaWestland AW101 Merlin MK4 is equipped with the largest cabin in its class. The aircraft is designed to perform missions in extreme environments such as the Arctic or the Antarctic. For combat, it is armed with anti-ship missiles and torpedoes, 12.7mm and 7.62mm machine guns, air-to-air missiles, and air-to-surface missiles.

Once deliveries are complete, the helicopters will be used to deliver enhanced capability for Royal Navy's Commando Helicopter Force.

"We still have a lot of work to do but when the program is complete the Commando Helicopter Force will have a very capable Commando Helicopter aircraft ready to fully operate in its maritime environment," O'Brien added.