Oct 13 (Reuters) - Honeywell International Inc (HON.O) said on Wednesday it will require employees at all its U.S. offices and some manufacturing locations to be vaccinated against COVID-19 under an executive order from President Joe Biden for federal contractors. Other government contractors including Boeing Co (BA.N), International Business Machines Corp (IBM.N) and Raytheon Technologies Corp (RTX.N) have also mandated vaccines, with the White House last month setting Dec. 8 as the vaccination deadline for millions of employees of federal contractors. "The vaccination mandate applies to all Honeywell locations within the U.S. and its territories that support U.S. government contract work. This includes all U.S. office locations," the conglomerate said. However, manufacturing sites not supporting government contracts are excluded from the mandate, Honeywell said. The company has 41,000 employees in the United States.U.S. defense contractor Leidos Holdings (LDOS.N) also said on Wednesday that its employees must be fully vaccinated or provide a negative COVID-19 test result to access the company"s facilities from Oct. 1. Ship and submarine builder Huntington Ingalls Industries Inc (HII.N) said a vaccine would be required to stay employed. "While we are discussing the effects of this mandate with our union partners, it will be a condition of continued employment for our workforce to be fully vaccinated" by December 8, Chris Kastner Huntington Ingalls" chief operating officer wrote in a memo to employees posted on a company website on September 29. Separately, Lockheed Martin Corp (LMT.N) recently updated the COVID-19 guidance on its website to say it would "follow federal, state and local mandates, including those requiring vaccinations."Previous versions of the guidance did not specifically address vaccination requirements.