5.45pm BST

With about half of its 800,000 civilian employees expected to be sent home without pay, the defense department stands to be hit particularly hard by a government shutdown. "We are now in a moment of regrettable and avoidable uncertainty," defense secretary Chuck Hagel writes in a letter to all department personnel, just released. Here is the letter in full:

Message to the Force on the Potential Government Shutdown

As Written by Secretary of Defense Chuck Hagel, Seoul, South Korea, Monday, September 30, 2013

To all Department of Defense personnel:

As you know, the government's annual funding could expire at midnight tonight. I have joined President Obama in urging Congress to prevent a lapse in appropriations, and like all of you I would be deeply disappointed if Congress fails to fulfill its most basic responsibilities. We are now in a moment of regrettable and avoidable uncertainty. It would be irresponsible on our part not to prepare for the possibility of a shutdown – especially given that we don't know what Congress will do over the next 24 hours.

To this end, DoD has been moving forward with necessary and prudent preparations. DoD leaders, in coordination with the Office of Management and Budget and the Office of Personnel Management, have been reviewing and updating contingency plans. Whatever happens, we will be prepared.

If a shutdown occurs, it will affect different parts of our department in different ways. While military personnel around the world would continue to serve in a normal duty status, a large number of civilian employees and contractors would likely be temporarily furloughed. Your supervisor will provide more information, but I want you to know that furlough decisions are dictated solely by the law, which only permits us to direct civilians to work if they are required to continue supporting military operations or if they are required to protect DoD personnel and property. The furloughs are in no way a reflection of the importance of your work, the hard effort you put forth every day, or your dedicated service to our department and our nation.

This has been a trying period for DoD personnel across the globe – military, civilian, and contractors alike. Right now, I am in South Korea meeting with our Republic of Korea allies and commemorating the 60th anniversary of our mutual defense treaty. I have spent time with U.S. troops and DoD civilians stationed here who would be impacted by a government shutdown. This is an unnecessary and unwelcome distraction from our mission of defending the nation.

DoD personnel and families have been through a lot recently. Sequestration has meant that most of our civilian employees have already had to endure furloughs this year, causing significant stress and hardship, while service members and military families have had to deal with the needless strain of reduced readiness as well as temporary reductions in services essential to their wellbeing. I know the uncertainty of a possible shutdown only adds to the anxiety that I'm sure many of you and your families are feeling. But I also know that the Department of Defense is a strong and resilient institution. We are going into this challenge together and we will come out of it together.

I want to thank all of you – military and civilian – for your patience and your professionalism, as well as your continued service and dedication to both our department and our country.

Thank you, and God Bless you and your families.

h/t Paul Lewis (@PaulLewis)