Royal Air Force and Luftwaffe jets with the Baltic Air Command intercepted a group of Russian aircraft, including a spy plane, on Tuesday.

Eurofighter Typhoon fighter jets operated by the United Kingdom and Germany intercepted Russian jets on Tuesday, with both air forces releasing images of the aircraft. Flying in formation over the Baltic were two SU-27 ‘Flanker’ jets escorting an Il-20 intelligence plane with their transponders off.

While military aircraft can fly without transponders — devices used to aid identification for air traffic control — it is generally considered best practice to leave them turned on unless actively engaged in war or clandestine activity. The photographs released by the NATO airforces clearly show the Russian jets with the now-familiar ‘Z’ wartime marking, as if there was any doubt as to who the fighters belonged to.

The United Kingdom and Germany are presently sharing command of the NATO Baltic air policing mission, a rotating pool of aircraft that launch to interrogate unidentified aircraft over the sea and deter incursions into sovereign territory. NATO executes this air policing mission using fighters from European nations because Latvia, Lithuania, and Estonia, which are NATO members which border Russia and Belarus, do not have fighter jets of their own.

As NATO themselves put it, the policing mission aircraft are “often launched to visually identify Russian Federation Air Force aircraft… They often approach or fly near NATO airspace without using transponders, communicating with Air Traffic Control or having filed a flight plan.”

Many of the flights intercepted — hundreds a year — are flights between the Russian Kaliningrad exclave in northern Europe, which can only be reached by air or sea from Russia. But others, as in this case with an intelligence aircraft escorted by two jet fighters, are less benign.

Germany said of the interception on Wednesday: “[Eurofighters] identified three military machines. Two SU-27 Flankers and one IL-20 from [Russia] flew without a transponder signal in international airspace over the Baltic Sea.”

This week’s interception closely parallels another such event in February when the same Russian formation was intercepted by a Dutch F-35.