Nine months into the war in Ukraine, Russia's military is virtually at a standstill.
The resistance of Ukraine's armed forces has shattered the illusion of Russian military might.
Lieutenant General (Retired) Ben Hodges spoke to Forces News about the five key lessons that he has learned from the Ukrainian counter-offensive.
Lesson 1: Modern warfare is still about the troops in the fight
According to the former commander of the US Army in Europe, lesson number one is that investment in the training of the forces is vital.
Modern warfare is still based on the human factor, and success is down to unit cohesion, he says.
"The importance of training, of leaders having the experience and ability and confidence to make decisions without perfect information.
"The stuff that we already know from our training and doctrine now is being reinforced even in modern warfare you have to have the human factors," Lt Gen Hodges said.
Lesson 2: Strategic planning is critical
The retired US Army general said that the amount of ammunition that has been used in this war has been "staggering".
During the Iraq war, Lt Gen Hodges commanded infantry units. His most recent operational assignment was as Director of Operations, Regional Command South, in Kandahar, Afghanistan.
"In 20 years of Iraq or Afghanistan, I never saw anything that comes close to that.
"Ammunition consumption from small arms to artillery to rockets to air and missile defence," Lt Gen Hodges said.
He pointed to how strategic planning might be critical to sustain the supplies that Ukraine needs in the conflict, saying: "The defence industry in none of our countries right now is operating at a level to sustain that."
Lesson 3: The requirement for air and missile defence has increased
During his time as commander of the US Army in Europe, the lieutenant general says he was worried about not having enough air and missile defences.
At that time, he said the thinking was about the need to protect airfields, seaports and critical infrastructure.
The Russian military has been targeting civilian infrastructure in Ukraine as well, firing multi-million dollar cruise missiles at apartment buildings and power stations.
Lt Gen Hodges said this means the requirement for air missile defence is now "significantly higher".
Lesson 4: Hybrid warfare remains relevant
Hybrid warfare aims to achieve strategic goals by targeting national vulnerabilities.
It can take the form of disinformation campaigns and fake news, meddling in foreign elections or deploying special forces on covert (secret) operations.
According to the retired commander, hybrid warfare in Europe is at its worst since the Second World War.
Lesson 5: Accurate intelligence is key to success
Lt Gen Hodges admits that he overestimated Russian capabilities, saying: "I was so wrong about Russian capabilities.
"I really thought the Russians would do better.
"I think many of us overestimated what they would be able to do.
"How did we get that so wrong?" Lt Gen Hodges asked.
The retired general also added that he was never doubtful or sceptical about Ukrainian capabilities.