On May 9, 2014, a 13-ton armored vehicle tore through pro-Russian barricades in Mariupol, launching a young battalion commander into Ukrainian legend as a symbol of raw, improvisational resistance.

Today, that soldier, Maj. Gen. Mykhailo Drapatyi, assumes command of Ukraine’s armed forces in a fraught moment of military and political transition, leading his country in a battle that could have scarcely been imagined a decade ago.

It is a war both of grinding attrition and high-tech innovation, where survival is dictated by which side can adapt faster and better integrate ever-evolving weapons into the daily slog of fighting under skies saturated with drones.

General Drapatyi, 43, who was appointed the top military commander by President Volodymyr Zelensky on Tuesday night, replaced the 60-year-old Gen. Oleksandr Syrskyi. General Drapatyi represents a newer generation of post-Soviet military leadership in Ukraine that has embraced more modern approaches to warfighting.

He is one of the key architects of Ukraine’s “drone line” strategy. Instead of relying purely on static trenches holding vulnerable infantry troops, Ukraine created a continuous “kill zone” behind the front line filled with attack and reconnaissance drones and automated turrets.

That tactic has helped slow Russian advances, allowing Ukraine to take the initiative along parts of the front for the first time in years. It has also given hope to a war-weary nation that has lost tens of thousands of soldiers.

While recent battlefield developments have been positive, especially with long-range strikes in Russia and Crimea, analysts warned that Ukraine must ensure a smooth handover in the military leadership to maintain momentum.

The challenge is heightened by the circumstances of General Syrskyi’s dismissal. He was ousted after protests about Mr. Zelensky’s firing last week of the reform-minded defense minister, Mykhailo Fedorov, whom the general had clashed with.

In an online commentary, Mick Ryan, a retired Australian general who is a fellow at the Lowy Institute, a research group in Sydney, wrote, “The danger now is that a change of command creates a period of uncertainty while new leaders find their feet, and Russian forces exploit it.”

“The new team’s first job is to make sure the reshuffle does not slow the tempo of operations at the front, deep inside Russia — or innovation inside the Ukrainian military,” he added.

General Drapatyi steps into a matrix of crises. He must address problems with Ukraine’s recruitment system, while also bracing for a possible renewed Russian mobilization effort. He must also shield energy grids from a winter strike campaign even as Ukraine’s most sophisticated air defenses run low on ammunition. And he must blunt Russia’s slow and bloody campaign to level the remaining bastions of defense in the Donbas region of eastern Ukraine.

There is also the crisis in civilian-military structure that was laid bare after Mr. Zelensky fired Mr. Fedorov. It is not clear what role the 35-year-old Mr. Fedorov will play going forward, but Mr. Zelensky has offered him other roles in the administration, and the president has said that the two men would meet again on Wednesday.

Mr. Zelensky said that he wanted to give Mr. Fedorov “a worthy leadership position that would allow him to bring together our country’s technological capabilities and ensure their continued development.”

For General Drapatyi, dealing with the president’s office will require a balancing act, analysts said, between asserting the operational independence favored by military reformers and accommodating Mr. Zelensky’s tendency toward direct battlefield management.

Unlike General Syrskyi, whose willingness to comply with executive directives made him a predictable partner for Mr. Zelensky, General Drapatyi is taking over with backing from a reformist movement demanding a departure from rigid, top-down command.

Valerii Zaluzhnyi, a former top commander of Ukrainian forces who was fired by Mr. Zelensky in 2024 after the two clashed over mobilization efforts and counteroffensive strategy, said in a statement that the task ahead of General Drapatyi was “much harder than he imagines.”

Liudmyla Buimister, an independent lawmaker who is a former special forces commander and still serves in the military, said she expected General Drapatyi to change the culture of the high command, stop the practice of micromanaging battlefield decisions and bring more coherence to the deployment of forces.

General Drapatyi is expected to champion many of the same technology-driven initiatives that Mr. Fedorov was pushing.

Jack Watling, an analyst at the Royal United Services Institute in London, wrote in an online commentary that, with the change at the top, Mr. Fedorov’s push for a data-driven approach to improve the military’s performance might now be possible.

General Drapatyi is also expected to empower commanders who have used technology to reduce casualties.

Like Mr. Fedorov, General Drapatyi is believed to see problems in internal processing, training flaws and corruption as reasons for the recruitment shortfall. Ukraine’s hope is that a change in culture in the high command will increase motivation to join the military.

“Already, we are seeing a boost in the morale of the people inside the armed forces and also in the general public,” Ms. Buimister said.

Liubov Sholudko and Nataliia Novosolova contributed reporting.