The US is worried that it’s submarine fleet is falling behind China and Russia’s as both countries aggressively push to expand and modernize their navies.

Admiral Harry Harris told the House Armed Services Committee on Wednesday that US Pacific Command “suffers shortage of submarines today, my requirements are not being met.”

And, according to Foreign Policy, Harris told the committee that his main concern was that the Pentagon was not managing to keep pace with its rivals in the region.

Harris directly linked this threat to the rising submarine powers of Russia and China.

Russia already has the second most capable submarine fleet in the world after the US, Harris admitted, and he warned that their capabilities were likely to rise in the coming years as the US submarine force falters.

Currently, Foreign Policy notes, the US Navy’s shipbuilding plan calls for a fall in the number of attack submarines from 52 to 41 by 2028 before “gradually clawing back to 50 by 2044.”

As the number of US submarines is expected to fall, China and Russia are expanding their submarine forces. Russia has expanded a naval base to allow for new ballistic-missile submarines in the Northern Pacific.

At the same time, Moscow has also undertaken a serious push for the expansion and modernization of its submarine fleet — including the introduction of new submarine models in both Europe and Asia.