Cavoli declined to discuss many specifics about the submarines outside of a classified briefing to House members, but he did give a glimpse of the operations during the public hearing.
"Russians are more active than we've seen them in years, and their patrols into the Atlantic and throughout the Atlantic are at a high level, most of the time at a higher level than we've seen in years," he told lawmakers. "And this is, as you pointed out, despite all of the efforts that they're undertaking inside Ukraine."
The Russian military has suffered staggering losses in the war in Ukraine, which Moscow started more than a year ago when it invaded its neighbor.
Estimates vary on the exact number of Russian troops killed or injured in the war -- recently leaked Pentagon intelligence reportedly places the number of Russian casualties between 189,500 and 223,000 -- but the losses have been high enough that Moscow has called up conscripts and taken steps to make draft dodging harder.
Despite the Russian losses and the fact that its military has so far failed to achieve any major objectives in the war, U.S. officials continue to warn that Russia presents an "acute" threat to American and European security.
Cavoli echoed that warning Wednesday, adding that while the Ukrainians are in a good position for an expected spring counteroffensive, Russia remains a formidable foe.
"The Russian ground force has been degenerated somewhat by this conflict, although it is bigger today than it was at the beginning of the conflict," he said. "The air force has lost very little; they've lost 80 planes. They have another 1,000 fighters and fighter bombers. The navy has lost one ship."
Celeste Wallander, the assistant secretary of defense for international security affairs, who was testifying alongside Cavoli, said it was "very unlikely" Russia could seize all of Ukraine.
But she also warned against underestimating the strength of the Russian military at this point in the war.
"Its conventional forces, ground forces that are in Ukraine, have been devastated," Wallander said. "Russia still retains strategic capabilities, an air force, cyber, underwater. ... We should not make the mistake of underestimating Russia's military capabilities because the stakes of getting it wrong are too high."