The craft, a U.S.-made Bell Boeing V-22 Osprey, is effectively a cross between a helicopter and a turboprop plane, which uses two Rolls-Royce Tiltrotor engines.

In takeoff and landing, it usually operates more like a helicopter, with nacelles vertical and rotors horizontal. Once aloft, the nacelles can rotate forward 90 degrees in a few seconds, to facilitate forward flight, and other orientations are possible.

It's not just a curio, however, and is in fact a heavily-armed transport craft operated by the U.S. Air Force, the U.S. Army, the U.S. Navy and the U.S. Marine Corps, usually sporting either a 7.62×51mm NATO (.308 in caliber) machine gun or a M240 machine gun or (.50 in caliber ) fixed on its loading ramp.

The version which flew over Tallinn on Saturday was, according to ERR's online Estonian news, the CV-22B

This variation is used by the U.S. Special Operations Command (USSOCOM) in long-range special operations missions, and is equipped with extra wing fuel tanks and more sophisticated radar and counter measures equipment than other types.

The CV-22B is in Estonia for around two weeks on a joint U.S.-Estonian Defence Forces (EDF) exercise.

If you missed it, further flights are planned across Estonia for that period. While lower altitude flights are reportedly planned further away from major population centers and are likely to take place in the evening, Saturday's flight, which took off from Tallinn Airport (see gallery), looked like it was below the 100-meter altitude, at a very layperson's estimate, flying roughly in a northwesterly direction over Rävala Street.

Japan's defense forces also have V-22s on order.

Download the ERR News app for Android and iOS now and never miss an update!