By Nathalie Tadena Lockheed Martin Corp. (LMT) said it has cut 740 jobs from its mission systems and sensors business, which the defense contractor said is part of its efforts to improve efficiency and affordability in a challenging budget environment. Lockheed Martin said it informed 308 U.S.-based employees Tuesday that they will no longer be employed by the company. In May, 432 employees left the business as part of a voluntary layoff program. The efforts have reduced the mission systems and sensors business' workforce by about 2%. Overall, Lockheed Martin has about 123,000 employees. "Reducing our workforce is a difficult but necessary decision to position our business for future growth and ensure we remain competitive," said Dale Bennett, president of Lockheed's mission systems business. The mission systems and sensors unit provides systems engineering, software development and program management for the U.S. armed forces, as well as industrial, research and medical customers. U.S. defense contractors have struggled to define the future size and shape of their operations due to uncertainty over Pentagon's budget cuts. Lockheed is viewed as one of the companies most vulnerable to cuts because of its role in large projects such as the Joint Strike Fighter, and last year said it would shed thousands of jobs amid the Defense Department's belt tightening. In April, Lockheed Martin reported a 20% rise in first-quarter profit as the world's largest defense contractor focused on cost and efficiency measures to counter the uncertain outlook for military budgets. Lockheed shares were off by 48 cents to $86.91 in recent trading. The stock is up 7.4% since the start of the year. Write to Nathalie Tadena at email@example.com.