(Reuters) - President Vladimir Putin's defence minister has appointed Russia's most senior general, Chief of the General Staff Valery Gerasimov, 67, to lead its war in Ukraine, the most dramatic in a series of senior command changes since Russia invaded in February.

CRITICISM

Many of the nationalist war bloggers who have licence from the Kremlin to criticise the conduct of the war have blamed Gerasimov for the fact that a superpower military - supposedly modernised and expensively re-equipped in the last 15 years - has failed so signally to subjugate its much smaller neighbour.

Critics in Ukraine, the West and even inside Russia cast the Russian armed forces as naive, poorly prepared and equipped, slow to react, and riven by disparate and often distant command structures.

After the failure of an unplanned mobilisation campaign to turn the tide in Russia's favour, rumours had swirled for months that Gerasimov, largely invisible to the public, would be sidelined.

Both Yevgeny Prigozhin, founder of the Wagner Group contract militia, and Ramzan Kadyrov, leader of the southern Russian republic of Chechnya, have made thinly veiled criticisms of Gerasimov while demonstratively claiming battlefield successes for their own, supposedly superior, semi-autonomous forces.

Supporters of the defence ministry say Russia often performs poorly at the start of wars, and that many of the problems that have become apparent in supply, technology and command over the past 10 months have been or are being resolved.

WHAT DOES IT MEAN FOR THE BATTLEFIELD?

The defence ministry said the seniority of the commander in charge of the "special military operation" reflects the expansion of its scale and the need to improve organisation and command.

Gerasimov's deputies will be Army General Sergei Surovikin, the previous theatre commander, appointed three months ago and nicknamed "General Armageddon"; Army General Oleg Salyukov; and Deputy Chief of the General Staff Colonel-General Alexei Kim.

Igor Korotchenko, a hardline military expert who is given generous space on state television, said Putin's decision stemmed from Ukraine's receipt of longer-range heavy weapons from the West and the prospect that it would soon receive Western armoured fighting vehicles and possibly battle tanks.

He said Gerasimov's arrival increased the likelihood that Russia might use battlefield nuclear weapons in Ukraine: 

"The appointment of Gerasimov means that all means of destruction in the arsenals of the Armed Forces of the Russian Federation - without exception - can be used."

Shoigu vowed on Tuesday to build a deeper arsenal of weapons, bolster aviation technology to better evade air defences and improve drone production.

WHAT ABOUT THE POLITICS?

By putting Gerasimov in direct command, Putin can send a signal to the West about his determination to win the war, reinforce the standing of the army relative to Prigozhin and