The commander in charge of overseeing the U.S. nuclear deterrent warned that the crisis in Ukraine is “just a warm-up” for future conflicts — and that Washington might not be prepared to meet the coming challenges.

“This Ukraine crisis that we’re in right now, this is just the warm-up. The big one is coming. And it isn’t going to be very long before we’re going to get tested in ways that we haven’t been tested [in] a long time,” said Admiral Charles Richard, the commander of U.S. Strategic Command. Richard made the remarks during an event hosted by the Naval Submarine League, according to a summary the Pentagon published last week.

He warned specifically that Russia’s use of nuclear blackmail against Ukraine right now is a “vividly illuminating” indication of how other countries might do the same in other conflicts. Some experts worry that Beijing could threaten the use of nuclear weapons as part of a bid to absorb Taiwan.

Richard also argued that U.S. military capabilities with regard to China are worrying, asserting that “the ship is slowly sinking.”

It is sinking slowly, but it is sinking, as fundamentally they are putting capability in the field faster than we are. As those curves keep going, it isn’t going to matter how good our [operating plan] is or how good our commanders are, or how good our horses are — we’re not going to have enough of them. And that is a very near-term problem.

Although the U.S. maintains dominance in submarine capabilities, Richard said that the U.S. needs to rapidly increase production, in keeping with previous U.S. weapons-acquisition efforts. “We need to bring some of that back. Otherwise, China is simply going to outcompete us, and Russia isn’t going anywhere anytime soon.”

Richard’s comments follow recent warnings by a number of U.S. officials that Beijing has accelerated the timeline according to which it might attempt to annex Taiwan by force. Secretary of State Antony Blinken recently said that those plans would likely take place on a “much faster timeline.”