Germany and France will launch a program this month to develop a new marine patrol and surveillance aircraft, the German Navy said on Friday, in what defense sources said was a response to a sharp increase in Russian submarine patrols.

German Defense Minister Ursula von der Leyen and her French counterpart, Florence Parly, plan to sign a letter of intent about the new Maritime Airborne Warfare System at the Berlin air show on April 27, it said on its website.

The two countries agreed last July to seek a "European solution" to replace existing marine surveillance planes, and develop a road map to that end by mid-2018. The letter of intent formalizes those plans and paves the way for both countries to harmonize their military requirements for the maritime mission.