The United States has improved the readiness of its underwater forces amid China's fast-growing navy, with none of its nuclear-powered attack submarines idle awaiting maintenance for the first time in over a decade, a report said on Monday. As the total number of SSNs decreased gradually, the maintenance backlog worsened following the outbreak of the COVID-19 pandemic. In fiscal year 2020, 10 submarines were in maintenance and five—the highest number recorded—were idle, accounting for 30 percent of the fleet. The U.S. SSN force currently consists of 20 Los Angeles-class, three Seawolf-class and 26 Virginia-class submarines, the report said. At least two Virginia-class vessels, USS Idaho and USS Massachusetts, are scheduled for official commissioning this spring.