WASHINGTON: Defense Secretary Leon Panetta vowed Friday to keep the US military the “strongest” in the world despite budget pressures, after being sworn in as the new Pentagon chief. “As your leader, I will ensure that our nation continues to have the best-trained, best-equipped, and strongest military in the world – a force prepared to confront the challenges that face us,” Panetta wrote in his first message to troops after taking the oath of office at the Pentagon. “Even as the United States addresses fiscal challenges at home, there will be no hollow force on my watch,” Panetta said. “That will require us all to be disciplined in how we manage taxpayer resources,” he said. Panetta pulled up in a motorcade for his first day on the job a little behind schedule, at 8:38 am local time (12:38 GMT), about eight minutes late. He walked to the Pentagon's entrance alone with no aides at his side, carrying a satchel. On the steps of the building, Panetta was greeted by a Marine officer who will serve as his senior military assistant, Lieutenant General John Kelly, whose son was killed last year in southern Afghanistan. “Welcome aboard sir,” said Kelly, shaking his hand. Officials said Panetta was sworn as the 23rd defense secretary at 8:48 am, succeeding Robert Gates who won praise from both parties during his four-and-a-half years on the job.