LONDON - Russia and its ally Belarus are carrying out exercises to practise the deployment of tactical nuclear weapons. 

What are these weapons, how might they be used and what do we know about the drills?

WHAT ARE TACTICAL NUCLEAR WEAPONS AND HOW POWERFUL ARE THEY?

Tactical nuclear weapons are intended for battlefield use, as opposed to strategic weapons designed to be fired across vast distances to wipe out enemy cities. The underlying physics is the same, using nuclear fission and fusion reactions to release vast amounts of energy. The destructive power of tactical nuclear weapons, while typically smaller than strategic weapons, is still comparable with the atomic bombs used by the United States to destroy the Japanese cities of Hiroshima and Nagasaki at the end of World War Two.

HOW MANY DO RUSSIA AND THE U.S. HAVE?

The United States has about 200, half of which are at bases in Europe. Russia has about 1,558 non-strategic nuclear warheads, experts at the Federation of American Scientists estimated in March. These could be delivered by different means including being dropped as bombs or fitted to a variety of missiles that are capable of carrying either nuclear or conventional warheads.    

WHAT DO THE RUSSIAN EXERCISES LOOK LIKE?

Russia said the first phase, conducted last month, involved Kinzhal and Iskander missiles. It took place in the southern region of Akhtubinsk, according to geolocation confirmed by Reuters. Video released by the defence ministry showed convoys of vehicles transporting Iskanders and presumably the nuclear warheads intended to be fitted to them. The warheads were blurred in the video. It also showed a Tu-22M Backfire bomber plane and a MiG-31K fighter, both capable of carrying the hypersonic Kinzhal. Video of the second phase on Tuesday showed an Iskander sy...