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A master-at-arms (MA) may be a naval rating responsible for discipline and law enforcement, an army officer responsible for physical training, or a member of the crew of a merchant ship (usually a passenger vessel) responsible for security and law enforcement. In some navies a “ship's corporal” is a position, not the rank of a petty officer who assists the master at arms in his various duties.
United Kingdom 
The master-at-arms is a ship's senior rating, normally carrying the rank of Chief Petty Officer or Warrant Officer, the MAA is in charge of discipline and is addressed as "Master" if holding the rank of Chief Petty Officer, even if the rating in question is a woman, she is still addressed as "Master" and known as the master-at-arms. The MAA is assisted by regulators of the Royal Navy Police, of which he is himself a member. He is nicknamed the "jaunty", a corruption of the French gendarme, or the "joss/jossman". The non-substantive (trade) badge of an MAA is a crown within a wreath.
British Army 
In the British Army, a master-at-arms is a commissioned officer of the Army Physical Training Corps posted as an SO2 or SO3 at divisional HQ or higher command, responsible for overseeing all fitness training in subordinate units. APTC Warrant Officers Class 1 fill the role at brigade HQs, while Warrant Officer Class 2 or staff sergeant physical training instructors are embedded at unit level. Master-at-arms is also an appointment in the Army Cadet Force, given to a cadet with the rank of cadet sergeant or above who takes command of drill on a divisional level.
|Issued by: United States Navy|
The Master-at-Arms rating started out in the post-American Revolutionary War on board the ships of the United States' early Navy. Taking on many customs and traditions of the Royal Navy, the existence of the rating did not take effect until the Naval Act of 1 July 1797 (a previous Act of 27 March 1794 authorized the same, but was allowed to expire) or known as the Congressional Act to provide for a Naval Armament, which authorized the President of the United States to provide four ships of 44 guns and two ships of 36 guns each, to be employed on each ship various officers, marines and petty officers under the command of a commissioned officer as the Captain.
"And be it further enacted, that there shall be employed, in each of the said ships, the following warrant officers, who shall be appointed by the President of the United States, to wit: One sailing-master, one purser, one boatswain, one gunner, one sail-maker, one carpenter, and eight midshipmen; and the following petty officers, who shall be appointed by the captains of the ships, respectively, in which they are to be employed, viz: two master's mates, one captain's clerk, two boatswain's mates, one cockswain, one sail-maker's mate, two gunner's mates, one yeoman of the gun room, nine quarter-gunners, (and for the four larger ships two additional quarter-gunners,) two carpenter's mates, one armourer, one steward, one cooper, one master-at-arms, and one cook." 
The call for a Naval armament, and the change of the United States' isolationism was in direct response to the hostile acts of the Barbary States' pirates. Because of this Congressional Act, the MA rating is recognized as one of the "oldest" ratings still existing in today's modern U.S. Navy. According to the Naval History and Heritage Command, the MA rating was officially established in 1797, disestablished in 1921, only to be re-established by the Chief of Naval Personnel on 1 August 1973, thereby making that date "August 1st" as the official birthday of the modern U.S. Navy Master-at-Arms.
Duties and functions of the Master-at-Arms 
In the United States Navy, an MA is the rating primarily concerned with law enforcement, and good order and discipline. They serve as a military police force onboard Naval ships and installations, both Continental United States (CONUS) and Outside Continental United States (OCONUS). MAs traditionally report to the Commanding Officer (CO) of the command, through the Executive Officer (XO) or Operations Officer (OPS), in maintaining good order and discipline, enforcing rules and regulations, and protecting life and property. MAs are personnel assigned to conduct LE (Law Enforcement) and ATFP (Anti-Terrorism Force Protection)duties, designated as Naval Security Force (NSF), would normally report within their chain of command to a military or civilian Security Officer (SECO). SECOs are commissioned Naval officers (649X/749X) or civilians who possess the necessary skill, training and/or experience to perform those duties. The MA rating is also supplemented by DoD personnel and contractors. Personnel in the MA rating can expect to see duties on board a variety of warships such aircraft carriers, cruisers and destroyers, aboard Naval shore and aviation installations, overseas in remote locations such as Bahrain and Diego Garcia, forward deployed to Iraq, Afghanistan or Africa, or assigned to Expeditionary or Naval Special Warfare (NSW) units. MAs are expected to perform their duties independently and advise their Commander or CO on matters pertaining to LE or ATFP.
Global War on Terrorism 
In support of the Global War on Terrorism (GWOT), today's MA force is being forward deployed to many places around the world including Cuba, Iraq, Afghanistan, and Djibouti, among other locations. MAs may be assigned to a Maritime Expeditionary Security Force (MESF), to Riverine Squadrons (RIVRON), Maritime Civil Affairs Groups (MCAG), or a special forces unit where they will conduct ATFP and expeditionary missions. These missions typically include protective services, VBSS Teams, and Embarked Security Teams (EST) aboard ships with minimal self-defense capability responsible for fortifying landside locations and securing foreign ports for use by U.S. warships. Most MAs who perform these type of ATFP related duties now report through the newly formed Navy Expeditionary Combat Command (NECC)  from their chain of command.
Since the beginning of the global war on terror efforts, the increased need for specialized units such as MESF and RIVRON units and the manning of several forward deployed locations such as Bahrain saw the need to increase the number of MAs. The current active duty number of MAs (approximately 9,000) is a direct reflection of that requirement. This was a significant increase from the previous manning level in the year 2000 which consisted of approximately 3,500 personnel.
Specialized training and education 
MAs perform a variety of duties that require specialize training that the average Sailor does not receive. They vary from LE duties which may include Military Working Dog (MWD) Handlers and Kennel Masters (NEC 2005/2006), Military Police Investigators (NEC 2002), Brig Afloat/Naval Corrections (NEC 2008), Patrolman, Gate Sentries, Physical Security Specialist, Small Arms Marksmanship Instructors (SAMI) (NEC 0812), Emergency Vehicle Operator Course (EVOC) instructor and Harbor Patrol. Various other training in support of the ATFP and Expeditionary missions may include training as an ATFP Training Supervisor (NEC 9501), or GWOT support roles such as Detention Operations (NEC 90DO) and Special Operations Support Team (90SP). MAs may also receive training from other U.S. military services and civilian agencies. These training may include Crime Scene Investigation, credentialing and certifications, or military customs inspection. MAs also receive training in various lethal and less-than-lethal weapons, combatives and self-defense techniques, and qualification in a variety of small arms.
MA "A" school is located at Lackland AFB, San Antonio, Texas. The civilian equivalent to MAs would be police officers, detectives, corrections officers, and port security personnel. MAs and NSF personnel receive formal and specialized training managed by the staff and personnel assigned to the Center for Naval Security Forces (CSF).
Various successful attempts to professionalize the MA rating have resulted in numerous credentialing offered by various accredited organizations and institutions. This in combination with rank, experience and training, along with specific requirements of the credentialing agency, may allow MAs to receive certifications. The U.S. Navy Credentialing Opportunities On-Line (COOL) defines this as "A continuously developing product for both active and reserve Navy service members that defines civilian credentials which best map to a Navy rating, job, designator, and collateral duties."  Just a few of the credentialing offered by various organizations in cooperation with the U.S. Navy COOL office include:
- American Board for the Certification in Homeland Security (ABCHS):
- CHS Levels I-V
- Certified in Disaster Preparedness (CDP-I)
- Anti-Sabotage Certified (ASC)
- Anti-Terrorism Accreditation Board (ATAB):
- Certified Anti-Terrorism Specialist (CAS)
- Certified Master Anti-Terrorism Specialist (CMAS)
Additionally, the U.S. Navy in cooperation with the U.S. Department of Labor have provided opportunities for MAs to complete certificates of completion in various apprenticeships. Such endeavor as stated in the United Services Military Apprenticeship Program (USMAP) website states, "The United Services Military Apprenticeship Program (USMAP) is a formal military training program that provides active duty Coast Guard, Marine Corps, and Navy service members the opportunity to improve their job skills and to complete their civilian apprenticeship requirements while they are on active duty. The U.S. Department of Labor (DOL) provides the nationally recognized "Certificate of Completion" upon program completion."  Apprenticeships offered by USMAP in cooperation with the U.S. Navy include:
- Police Officer I (Government Service)
- Correction Officer (Government Service)
- Security Specialist
- Master Homeland Security Specialist
- Computer-Peripheral-Equipment Operator (Clerical)
- Office Manager/Administrative Services
- Protective Service Specialist
MAs who have also met certain pre-requisites, training, experience and time in service and paygrade may also seek an advanced career path as a Naval officer. The opportunities for increased Naval service as a commissioned officer for MAs exist in any field that the particular MA is qualified to serve, although most seek a continued career in their current field as an MA through the Limited Duty Officer (LDO) and Chief Warrant Officer (CWO) commissioning programs. Those who choose this career path will perform various duties in the billet that they are assigned to, but most will serve as SECOs on major Naval installations and operational units.
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Notable Masters-at-Arms 
Medal of Honor Recipients 
- Master-at-Arms Robert T. Clifford, American Civil War, 22 August 1863
- Master-at-Arms William M. Carr, American Civil War, 5 August 1864
- Master-at-Arms James Seanor, American Civil War, 5 August 1864
- Master-at-Arms August Ohmsen, Interim 1871-1898, 21 August 1884
- Chief Master-at-Arms Daniel Montague, War with Spain, 2 June 1898
- Chief Master-at-Arms John Stokes, Philippine Insurrection, 31 March 1899
- MA2(SEAL) Michael Monsoor, Operation Iraqi Freedom, 29 September 2006
- MA2(EXW/SW) Christopher Drummonds. Served from 2000-2013, but was processed out of the Navy due to his higher tenure.NOT ON THE OFFICIAL CMOH LIST.
- Naval Act of 1 July 1797, Retrieved from the Library of Congress
- Enlisted rating in the U.S. Navy 1775-1969 retrieved from the Naval History and Heritage Command website
- BUPERSNOTE 1440 CH-1 dated August 17, 1973 retrieved from the Bureau of Naval Personnel webpage
- MILPERSMAN 1440-010 (para. 9 and 15), Change in Rating Authorization. Specific details on the conversion to the Master-at-Arms rating and minimum requirements.
- NTTP 3-07-2.3, Law Enforcement and Physical Security for Naval Installations
- General description of the duties of MAs world-wide as described on the Bureau of Naval Personnel (BUPERS) MA Community Manager's website
- NECC Webpage
- Center for Naval Security Forces wepage on Navy Knowledge Online (NKO)
- U.S. Navy COOL website
- The American Board for Certification in Homeland Security website
- The Anti-Terrorism Accreditation Board website
- United Services Military Apprenticeship Program
- OPNAVINST 1420.1, Enlisted to Officer Commissioning Programs Application Administrative Manual
- Congressional Medal of Honor Society