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USS Guardian (MCM 5) and the Navy’s Post-World War II Minesweepers

USS Guardian (MCM 5) sits aground on the Tubbataha Reef.  U.S. Navy photo 130129-N-ZZ999-033.

USS Guardian (MCM 5) aground on the Tubbataha Reef. U.S. Navy photo 130129-N-ZZ999-033.


By Captain George Stewart, USN (Retired)

On 17 January, 2013, the USS Guardian (MCM 5) ran aground on Tubbataha Reef in the Philippines. The ship had gotten underway after a port call at Subic Bay. An investigation by US Naval authorities came to the conclusion that it was not practical to salvage the ship and that it would have to be cut up into sections and scrapped. This article provides additional background information concerning the ship and additional insight as to why this decision was necessary.

USS Guardian (MCM 5) is one of 14 Avenger Class Mine Countermeasures ships that entered service between 1987 and 1994. At the time they were authorized, these were the first large ocean going minesweepers to be built for the navy in 25 years. Due to problems experienced during the Korean War with steel hulled World War II era minesweepers, the navy undertook a major shipbuilding program during which 58 ocean minesweepers (MSO) entered USN service between 1953 and 1958. In addition 27 more of these ships were provided to foreign navies. The Avenger Class MCM design shared many common design features with the earlier MSOs including wooden hulls and non-magnetic diesel engines.

Guardian itself was built by Peterson Builders at Sturgeon Bay, Wisconsin and it was commissioned on 16 December 1989. It is home ported in Sasebo, Japan. The ships have the following major characteristics:

  • Displacement (Full Load) – 1312 tons
  • Length – 212’9”
  • Beam –  38’11”
  • Draft – 11’3”
  • Propulsion –4 diesel engines – twin controllable pitch propellers, 2400 BHP
  • Maximum Speed – 13.5 knots
  • Range – 2500 nm @10 knots
  • Personnel – 83 (7 officers and 76 enlisted)

The basic hull design is similar to that of the previous MSO classes built in the 1950s. The hulls are constructed of fiberglass sheathed wood in order to minimize their susceptibility to magnetic mines. This was probably the major factor in the determination as to whether or not Guardian could be salvaged.

The propulsion system is twin screw. Each package consists of a pair of non magnetic diesel engines driving a controllable pitch propeller via a reduction gear. Each package also contains a 200 HP electric trolling motor that is used for low speed quiet operation. The electrical plant includes a pair of 375 kW ship service diesel generator (SSDG) sets and a single 1750 kW gas turbine driven generator that provides DC power for magnetic minesweeping operations.

The reliability of non magnetic diesel engines has been a continuing problem for the Navy over the years. One problem has been finding an engine manufacturer who is willing to establish a production line for these engines because of the limited number of orders associated with a shipbuilding program. The majority of the 1950s built MSOs were originally fitted with Packard Model 1D1700 diesel engines. Due to problems experienced with these engines a major re-powering program was implemented during the 1960s and 1970s to replace them with Waukesha Model L-1616 engines. Originally it was planned to power the Avenger Class ships with Italian made Isotta-Fraschini (IF) Model 1D 36 engines. However due to production delays and problems encountered with these engines it was found necessary to fit MCM 1 and MCM 2 with surplus Waukesha engines left over from the previous MSO re-powering program. In order to utilize these engines it was found necessary to send them back to the vendor in order to obtain correct shaft rotation. This caused delays in the program. It is understood that reliability problems have continued to be experienced with the IF engines in service.

Basic minesweeper design features are driven by the ability to sweep three different types of mines:

  1. Moored Mines – These type of mines require direct contact with the ship’s hull for detonation therefore they must be located relatively close to the surface and anchored to the bottom with cables. The Avenger class ships are fitted with Oropesa (O-Type) sweeping gear consisting of a pair of long wires fitted with cable cutters which are towed behind the ship. When a mooring cable is cut, the mine will bob to the surface where it can be destroyed by gunfire. This type of sweep gear dates back to the World War II era.
  2. Magnetic – These mines rest on the bottom and are detonated by variations caused by a ship’s magnetic signature as it passes overhead. They are swept by means of an electrical cable (referred to as a “tail”) which is towed behind the ship. The “tail” is supplied with pulsed DC electrical current from a generator located on the ship. The Avenger Class ships are each fitted with a 1750 kW gas turbine driven generator for this purpose. Major design features, including the wooden hull and the use of non magnetic engines and other equipment are driven by the requirement to minimize the vulnerability of the MCM to magnetic mines.
  3. Acoustic – These mines also rest on the bottom and are detonated by underwater noise from a ship passing overhead. They are detonated by devices called “acoustic hammers” towed by the minesweeper. Resilient mounting, similar to that found aboard submarines or ASW surface ships is used to minimize the acoustic signature of the MCM as it passes through the water.

Magnetic and acoustic mines are provided with “Ship Counts” which require a number of ship passes overhead in order to detonate. For this reason, it is necessary for the MCM to make multiple passes over a mine field in order to ensure that all mines are detonated.

Mine countermeasures ships are also provided with variable depth sonar (VDS) to assist in locating mines. A more recent development is the use of underwater submersibles referred to as Mine Neutralization Vehicles (MNV). The mine neutralization vehicle is a self-propelled remote-controlled submarine. The vehicle’s low acoustic and magnetic signature makes it virtually invisible to even the most modern sea mines. The Mine Neutralization Vehicle is the primary subsystem of the Navy’s AN/SLQ 48 Mine Neutralization System (MNS). Each sensor package consists of a mine-hunting sonar and two television cameras. In addition to the vehicle, MNS consists of an Umbilical Cable Handling System (UCHS), Vehicle Handling System (VHS), shipboard power supply, and associated control consoles. The system works in conjunction with a shipboard mine hunting sonar and precise inertial navigation system. The MNVs carry explosive devices which are capable of detonating bottom mounted mines and they also can cut the cables of moored mines. The MCM 1 Class ships are each fitted with a pair of MNVs. They are also capable of conducting the conventional mine sweeping operations previously discussed.

Prior to 1991 the Atlantic force minesweepers were home ported in Charleston, South Carolina while the West Coast ships were in Long Beach, California. In 1991 the decision was made to move the entire minesweeping force to Ingleside, Texas. At one time the majority of the MCM 1 Class ships were based there. Because of the limited range of the ships, this did not prove to be a satisfactory arrangement. In a number of cases it was necessary to transport the ships to their operating areas by means of heavy lift cargo ships. The Naval Vessel Register now shows the following home port assignments for the MCM 1 Class Ships:

  • Sasebo, Japan – 4 ships
  • San Diego – 5 ships
  • Bahrain – 4 ships
  • Ingleside – 1 ship

The wooden hulled minesweeping program was originally inspired by the back to back losses of the steel hulled USS Pirate (AM 275) and USS Pledge (AM 277) both of which were sunk by mines off Wonsan, North Korea in 1950. Guardian represents the fifth loss of a wooden hulled ocean going minesweeper since that time. The others were:

  • USS Prestige (MSO 465)  – 1958 – Grounding in Japan
  • USS Stalwart (MSO 493) – 1966 – Fire and capsizing in San Juan
  • USS Avenge (MSO 423) -1968 – Fire – Shipyard in Baltimore
  • USS Force (MSO 445) – 1972 – Fire  off Guam

At least five other ships of the class suffered significant damage from engine room fires but it was possible to restore them to service.

Helicopters have been used for some minesweeping operations. The MH 53E Sea Dragon helicopter can be used to tow a sled containing the actual minesweeping equipment. However there are limitations due to endurance and the requirement for a “mother ship” to actually stream and recover the equipment.

The future of the US Navy mine warfare program is uncertain. It is understood that the intent is to provide mission packages which can be used by the littoral combatant ships for mine countermeasures operations. However at this time no new vessels specifically devoted to mine warfare have been authorized.

George W. Stewart is a retired US Navy Captain. He is a 1956 graduate of the Massachusetts Maritime Academy. During his 30 year naval career he held two ship commands and served a total of 8 years on naval material inspection boards, during which he conducted trials and inspections aboard over 200 naval vessels. Since his retirement from active naval service in 1986 he has been employed in the ship design industry where he has specialized in the development of concept designs of  propulsion & powering systems, some of which have entered active service. He currently holds the title of Chief Marine Engineer at Marine Design Dynamics. He served as Executive Officer of USS Force (MSO 445) between 1959 and 1960.


  1. Ships and Aircraft of the US Fleet, Polmar, 2005
  2. CHINFO Photo Album
  3. MSO Casualties, Navy MSO Association
  4. Naval Vessel Register



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  1. Frank DeMasi

    I have a very hard time matching the picture to the article. The article is clearly a short history of US Navy minesweepers since about 1950 and does allude to minesweeper losses since then. There is a little information on the Guardian grounding but really not enough to justify the picture or the headline. Additionally the article does not touch on one of the more critical aspects of the decision to not save the ship, that is the environmental impact of such an operation. I think you have done a disservice to the crew of Guardian who fought hard to save their ship in the face of an overwhelming sea. It’s hard to beat the ocean. For the record I served in USS Inflict and have operated in and cleared live minefields in the Persian Gulf

    • Admin

      Mr. DeMasi,

      We are sorry you feel that way. This is a guest post from Captain George Stewart, one of our blog volunteers with a vast knowledge of the subject area. If you would like to address him with your opinions and/or grievances directly, please let me know. We want to ensure that the service and sacrifice of the Navy is always the most important message we broadcast.


      Matthew T. Eng
      Digital Content Developer
      Naval Historical Foundation

  2. keith dewitt reid

    I googled MSO 1and2, which were stationed at Charleston Naval Base behind MOMAG(Mobile Mine Assembly Group) from 1971-to1973. These were mine sweepers which had hulls packed with styrofoam, control rooms mounted with shock absorbers. These ships had the largest outboards in the world that became usable when parts of the ships hull were flooded with sea water which lowered the props in the ocean when they were sweeping mines. These ships also had internal engines that drove conventional propellers when the hull was not flooded. I was a mineman(only 3400 since 1944). Active duty 1971-1973 and served on the USS Kitty Hawk CVA-63(attack aircraft carrier which was over 1000 feet long. Agent Orange exposed. Decorated US Navy Vietnam veteran. Keith Reid.

  3. Thomas Russo

    Any history on USS Alacrity would be appreciated as I left that sweep 1971

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