Twin.

This is coolbert:

I have always thought this warplane to be and oddity and curiosity of which there was no real usefulness. But I am wrong! An expedient design [?] but nonetheless successful to a degree.

The P-82, later F-82 Twin Mustang. Long-range escort fighter and air defense interceptor.

A warplane as described by an acknowledged aviation authority:

"Long range fighter to be used with B-29s on missions where the single cockpit Mustang didn't have the range. Didn't arrive before the end of WWII and Iwo Jima negated the need for a super long range fighter--numerous P-51 squadrons were now based there to escort the B-29 Tokyo raids."

"Extra pilot to give the other some rest.  Later plans included long range escort for B-50 and B-36 nuclear operations. Shot down the first enemy aircraft (3) in one mission over Korea.  (Lagg-9, Lagg-11, unknown)"

"Betty Jo" as on display at the National United States Air Force Museum, Dayton, Ohio, USA. Established distance and speed records for a propeller-drive aircraft that still stand!

Yes, two P-51 Mustang joined. Two engines, two pilots, two tails, one and one-half wing per plane. A heavy-fighter warplane concept similar to the American P-38 [P-38 having only pilot]. Allowed for long-range bomber fighter escort all the way to the target and back again. Also useful as an interceptor in the traditional mode in areas of the world where airfields few and far in between [such as Alaska].

Method of attack [similar if not downright identical to the American P-38] once again as described by acknowledged aviation authority:

"Start the attack from above, at high speed, dive through the enemy formation firing that concentrated cone of fire from guns and auto cannons, and keep going, zooming up to altitude to sit on the perch and contemplate the error of your last attack. From the perch, like a patient hawk, you were supposed to choose your fights, not just flip on down to turn and burn with the others.  That is not what your plane was designed to do."

The F-82/P-82 performing yeoman service in those immediate years after World War Two, and the only warplane able to escort Strategic Air Command bombers to the target and back again.

And thank you acknowledged aviation authority! You input and insight appreciated.

coolbert.