IAFM - Ship Types - Frigate Platform Dock (FPD-150)


The Frigate Platform Dock (FPD-150) is the most flexible ship in the IAFM.  It came about when I was mulling over how to provide enough escorts for SAGCOMs and CVCOMs, while still supporting forward deployed Marine forces.   The existing US Navy force model splits amphibious vessels (LPD, LSD, LHD/A) and escorts into distinct pools. However you still have to provide escorts for ESGs as well as CVBGs.  But if you look at a modern amphibious ship, like the LPD-17, the systems aboard aren't that far off from those on a frigate.  It has an air defense radar, short-range SAM systems and C4ISR.  

So my thought was, why not smash together the capabilities of a guided-missile frigate and a modest-sized LPD and make a self-escorting "Frigate Platform Dock"?  This way, every ESG is always self-escorting.  Also, an ability to perform strike with VLS-based munitions, and Naval Surface Fire Support (NSFS) with Multiple Launched Rocket System (MLRS) and the gun mount.  

There is also discussion about using amphibious ships in non-traditional roles that cater to their size and flexible spaces.  In fact, a ship with LPD characteristics could be the ultimate modular vessel.  The Littoral Combat Ship modularity ultimately failed because the LCS's couldn't carry the weight and crew desired for different modules.  The FPD, on the other hand, excels at carrying weight and crew.  


The FPD-150 is a variant of the SC-150 family of vessels.  It shares common components such as propulsion, hull sections, electronics, and sensors with other variants.  It has a unique stern section housing the well deck.  All variants have unique internal arrangements and unique topsides, but share subcomponents whenever feasible.  The SC-150 family borrows sensors and combat systems heavily from the Constellation class FFG(X).  The FPD-150 is no different.  COMBATSS-21, EASR, SQQ-89, and so on, all are lifted directly from the FFG(X).  For its LPD nature, I used the Navantia Galicia class LPD as a size and capacity reference.   Galicia is considerably smaller than the LPD-17 class, but the IAFM makes up for size with numbers (48 FPDs vs ~20 LPD/LSDs in the current force). So in essence,

The FPD-150 is significantly longer (184m vs 160m LOA) and larger (>15,000t vs 13,000t) than the Galicia, with similar beam and draft.  This allows for more space for the combat systems, as well as a finer hull to reach task force speeds.  

Primary Sensors

The FPD reuses the FFG's primary air defense radar, SPY-6(V)3.  It is composed of three, fixed face, S-band, AESA radars.  Each face is composed of nine Radar Module Assemblies (RMAs).  According to reports, this relatively small radar has the equivalent sensitivity (thus range) to the DDG-51's SPY-1D(V) radar. 

I included a hull sonar on the FPD-150, where the FFG(X) does not have one.  Even though the VDS/towed array are significantly more capable, there are times where these sonars are not operational, especially on the FPD-150, where the Tactical ASW module isn't carried all the time. The hull sonar provides an always available back stop, persistent torpedo detection, and allows for multi-static operations with the VDS.  I don't see the need for a massive SQS-53B, but a smaller, presumably cheaper, sonar like the Thales BlueMaster sonar would work.  This sonar is integrated on some FREMM variants.

(U.S. Navy photo by Electronics Technician 2nd Class William Weinrich, Public domain, via Wikimedia Commons)

Internal Capacities

The FPD internal capacity is based off of the Galicia class.  From here.

Using a foreign design for sizing obviously doesn't consider US requirements.  US Marine ground force structures will have to adapt to fit.  Given the drive towards smaller Marine units for EABO and distributed operations, this may not be a large constraint.  The IAFM includes far more FPDs than the current US fleet architecture includes LPD/LSDs (48 vs ~20), so there's still plenty of room for Marines in the IAFM.

The flight deck and hangar are similar in size to Galicia.

It has hangar space for six MH-60s, four larger helicopters like the EH-101 (perhaps used for MCM), or two very large helicopters such as the V-22 or CH-53K.  


  • 64 x strike-length Mk 41 VLS cells in the bow
  • 2 x Mk49 RAM launchers
  • 1 x Mk45 Mod 4 5" gun (or new 155mm "No Rocket Science" mount)
  • 2 x Mk41 Mod 1 30mm cannons
  • 4 x Naval MLRS (NMLRS) launchers
  • 8 x Naval Strike Missile launchers (optional)
The FPD carries a respectable VLS cell battery of 64 strike-length Mk41 cells.  It doesn't use the larger Mk57 cells to conserve space and weight, so it won't be able to fire NGCM.  It will have to make due with Tomahawk, QPCM, and the Standard missile family (SM-2/3/6), ESSM, and VL-ASROC.

Naval Multiple Launch Rocket System (NMLRS)

The most controversial armament is the Naval Multiple Launch Rocket System (NMLRS), derived from the land based M270 MLRS. 

The video above shows the M270 launch system and pod reloading.  

A long history of Marine calls for improved naval fire support led to the aborted development of the DDG-1000 Zumwalt class.  The DDG-1000 designers unfortunately chose the most complicated way to meet the range requirements: a gun-launched missile (LRLAP).  In contrast, FPD adapts for use an in-service system and munitions under active development.  

For NMLRS, only the trainable launcher is retained.  The vehicle portions are not necessary.  The FPD-150 incorporates four of these launchers on the roof of the deckhouse, amidships.   The reloading sequence can take up to 5 minutes.  This low rate of reloading is made up for by the ability to fire off all twelve rockets per launcher in under a minute.  The launchers themselves should be pretty simple to develop, have low weight, no deck penetrations, and modest cost.  They're basically a box with a train and elevation system.  The naval variant will have to cope with vessel movements, but this should be a minor enhancement.  Rocket exhaust may need to be vented upwards, but this too isn't a major technical challenge.  Some fragmentation armor may be desirable to prevent sympathetic detonation of rocket pods in case of battle damage.  

Navalizing MLRS was considered in the past.  I haven't found definitive reasons why it hasn't been adopted, but rumors include difficulty of stowing and managing the large pods in confined warships, potential damage from caustic exhaust gasses, and HERO/IM compliance.  For the FPD, managing and stowing pods is not a major issue, given its size and magazine spaces.  It is not a cramped traditional warship.  It has a lot of open space by design.  It will use shared magazine spaces with Marine munitions.  When operating as a primary NSFS ship, vehicle decks can be used to stow additional pods.  Exhaust gasses and residue are managed with a washdown capability and perhaps fans to evacuate exhausts between firing.  

There may be a need to certify MLRS ordinance for HERO/IM compliance to fire from ships, but they are already carried aboard amphibious ships, and HIMARS has been test fired from the flight deck of an amphibious ship.  I haven't read of any show stoppers.

(USNI News)

Pods are brought up from the magazine via elevators to the rooftop launchers, where a crane moves them into place for the launchers.  Spent pods are moved back down in a reverse of the process (perhaps being thrown overboard in wartime).   This may not be as fancy or fast as some might want, but 8 pods in 4 launchers permits up to 48 shots before reloading.

Extended range GMLRS munitions will reach 150+km, with a 190lb warhead, or over 500km with the long range Precision Strike Missile (PrSM).  This allows the FPD to stand off at safe distances while still providing precision, volume fires ashore.  The Army and Marines are also considering adding an anti-ship weapon to MLRS.  Possibilities include the Naval Strike Missile or a variant of PrSM with terminal guidance.

A new, loitering munition should be added, like the now defunct MBDA Fire Shadow.

Fire Shadow (ThinkDefence)

This type of hybrid UAV/weapon gained prominence in the recent Nagorno-Karabakh conflict between Azerbaijan and Armenia.  Azerbaijani Harop loitering munitions were used to take out all manner of battlefield targets.  Loitering weapons have the ability to stay on station for a period of time, searching for targets, before kamikaze striking them. Fire Shadow could remain aloft for up to 6 hours.

An ASW rocket-powered depth bomb is another option.  The CSBA suggested something like this in their paper, "Sustaining the Undersea Advantage: Disrupting Anti-Submarine Warfare Using Autonomous Systems".  The Russian RPK-8 system is a useful example.  It is as a short-ranged system in the mold of the old Squid and Hedgehog launchers of WWII fame, but has a guided munition (90R1) that searches in a cone under itself as it sinks, and can deflect to engage targets it finds.  From here,

Tuchkov explains: "The rocket is aimed at its target (vessel or torpedo) using information about its location received from the ship's sonar station. After splashdown, the gravitational projectile separates and, with the aid of an acoustic homing head, finds its target and directs itself toward it. The 90R has a contact fuse." The 90R1, meanwhile, features an inductive noncontact fuse what goes off when the projectile reaches a certain predetermined distance from its target, thus further improving its efficiency.

The RPK-8 system is short ranged, only 4.3km.  An MLRS-based system could have much greater range and accuracy, possibly using the existing GMLRS rocket as the starting point, or the Boeing/Saab GLSDB rocket, which carries a winged SDB bomb.  Just replace the bomb with the guided gravitational projectile. This leverages the 360-degree engagement capability afforded by the wings.  

Mission Modules

Anti-Submarine Warfare (ASW) - Tactical

The FPD has a built-in hull sonar, and can house and operate towed sonars in the well deck.  It isn't limited to LCS-sized or destroyer-sized towed sonars, it has the capacity to carry multiple towed arrays,  VDSs, and/or larger arrays. It can carry six MH-60Rs, which contributes significantly to the voracious appetite for task forces ASW sorties.   Its internal spaces allows carriage of large quantities of sonobuoys and ASW munitions.  Future semi-disposable sensors, such as the Boeing SHARC Wave Glider, could be carried, deployed and recovered.

Anti-Submarine Warfare (ASW) - Theater

Given their large payload capacity, FPDs could carry a modular variant of the Surveillance Towed Array Sensor System (SURTASS).  The Vertical Line Array portion may not be straight forward to adapt for well deck deployment, but the multiple towed arrays could be.  


Additionally, the FPD could carry and deploy future semi-fixed sensor arrays like the buoy-based Affordable Mobile Anti-Submarine Warfare Surveillance System (AMASS).

FPDs with these module components wouldn't operate directly with task forces, but would provide self-escorting, long-range cueing and surveillance.  This would supplement existing unarmed SURTASS ships, rather than replacing them.  There's still a place for a purpose-built, unarmed vessel here.  It is less provocative, and the SWATH hull of the USNS Impeccable class has superior acoustics to a blocky monohull like the FPD.  However, if our T-AGOS ships are harassed, as the Chinese have done in the past, we could chose to send an FPD instead, with its greater size and warship demeanor.  

Marine Air Ground Task Force 

Obviously a main role for the FPD is to replace dedicated amphibious ships like the LPD-17 San Antonio class.  The FPD is certainly smaller, and can't carry as much as the LPD-17, but it does still have significant capabilities to carry Marines and their gear.  The IAFM includes over twice as many FPDs as the current Navy includes LPD/LSDs, so many of the issues of capacity can be resolved by aggregating multiple FPDs.  If we choose to keep the current MEU-sized Marine Air-Ground Task Force (MAGTF), a full squadron of four FPDs with a supporting CVCOM (CV55 and CG-150), is certainly large enough to carry it, and more. However, I would look to coming up with smaller, more numerous MAGTFs.  

I would move away from relying on the huge and expensive MV-22 as the primary rotary lifter for Marines.  Consolidate existing MV-22s into specialized squadrons that can deploy on CV55s or on land for situations that demand their high speed and long range.  MV-22s could also deploy, in more limited numbers on FPDs and CVLs.  Instead, Marine MAGTFs would use the MH-60S and CH-53K as their primary lifters.  The MH-60S is much smaller and a quarter of the price of an MV-22, but can still carry a full Marine squad.  It doesn't suffer from the same degree of brown out or brush fire-starting issues, and can land or fast rope Marines into tighter locations.  The Marines can take advantage of improvements to the entire H-60 family, used by all services, including more powerful, fuel efficient engines.  

This doesn't necessarily mean Ship To Objective Maneuver (STOM) is dead, but it is relegated to situations where we want to send a MAGTF-configured CV55.  

A single FPD could carry a reinforced company or two, or up to a battalion (minus).  Six MH-60S helicopters are enough to lift a platoon at a time, with a couple helicopters in reserve or used as armed escorts.  Its well deck could carry two LCACs or SSCs, up to four LCM-sized landing craft, or enough ACV/AAVs to land a company (~14-20).  

Mine Countermeasures (MCM) 

In the '60s, the Navy experimented with two Mine Countermeasures (MCM) support ships, USS Catskill (MCS-1) and the USS Ozark (MCS-2), each carrying 20 small, minesweeper launches (MSLs).  These MSLs were too small and lacked seaworthiness to be a viable system, but the concept of a mothership deploying a group of smaller boats (or USVs) to perform MCM is sound.  MCM is inherently parallelizable.  The more platforms hunting or sweeping, the faster it will go.  

The National Research Council released a study entitled, "Naval Mine Warfare - Operational and Technical Challenges for Naval Forces".  In it, they recommend an MCS-like vessel with the following characteristics,

The ideal support ship should have a flight deck and a well deck and be able to transport, at fleet speeds, the number of the small SWATH MCM platforms tailored to clearing the necessary number of lanes in a specified time (perhaps up to 10, if space is available in the well deck), and a similar number of MH-60S (or more capable follow-on) airborne MCM helicopters. Additionally, serious consideration should be given to providing space to carry the VSW detachment and mammal systems, along with UUVs when they become available.

The small SWATH platform they envisioned was the MHS-1.

Box 5.1 MHS-1 Characteristics

• Length

44 ft

• Beam


• Draft

4.5 ft

• Weight

24.0 long tons full, 21.4 long tons light

• Speed

18 knots

• Range

750 nautical miles at cruise (7 knots)

• Endurance

107 hours

• Propulsion

Two Caterpillar marine diesels (Mod. 3116 DITA 255 hp)


However, there are a variety of Unmanned Surface Vessels such that could be used instead of, or in addition to, an MHS-1-like vessel.

The FPD's well deck is large enough to carry eight MHS-1s.  It's hangar is large enough for six MH-60 helicopters or four EH-101 MCM helicopters.  This fits well within the NRC concept for an MCS.  FPDs with the MCS module augment the dedicated MCMV class in the IAFM, when there's a need for greater clearance rates close to shore.

Mine Warfare

With large interior spaces, payload capacity, and well deck, the FPD can be used to seed minefields with bottom or moored mines.  The US Navy doesn't currently maintain stocks of surface vessel-laid mines, but a significant stock of modern mines could be kept at modest cost.  Possible uses include rapidly reinforcing defense of Marine EABO bases, assisting Taiwanese defenses in a run up to conflict with China, or cutting off choke points with ASW and ASuW minefields are possible uses. Self-burying mines like the Manta below caused significant damage to the USS Princeton in the Persian Gulf during Operation Desert Storm.

AIAA Manta and Swedish Rockan bottom influence mines

It could even carry stocks of my speculative Unmanned Mine Delivery Vessel (UMDV), a low profile unmanned boat carrying up to 2,000lbs of mines out to a range of up to 700nmi.  

MH-60S's on the FPDs could carry the M139 Volcano mine dispenser system to rapidly set beach or inland minefields.

M139 Volcano System (US Army)

The Volcano uses modified Gator mines, the same that were developed to be dropped by aircraft inside the CBU-78/B (Navy) and CBU-89/B (Air Force). The entire system is made of four main components, which are the mine canister, the dispenser, the dispenser control unit (DCU) and the mounting hardware. The latter includes a jettison subassembly to be fitted to the Black Hawk to detach and propel the racks and canisters away from the aircraft in the event of an emergency.


The M-139 uses M87 and M87A1 mine canisters which contain five Anti-Tank (AT) mines and one Anti-Personnel (AP) mine or six AT mines, respectively, plus a propulsion device to scatter them 35 to 70 meters away from the helicopter. The mine canisters are capable of dispensing mines with 4-hour, 48-hour, and 15-day self-destruct timers.

Navy Expeditionary Combat Command (NECC) / Marine Riverine Support

During the Vietnam War, the Navy and Coast Guard conducted Operation Market Time and Operation Game Warden, two coastal and riverine efforts to stem the flow of troops, materials and supplies from North Vietnam into South Vietnam.  They used a wide variety of small boats, cutters, converted landing craft, and other vessels to provide coverage.  They used amphibious ships as mobile logistics hubs for these small vessels.  

USS Harnett County (LST-821)
 http://www.navsource.org/archives/10/16/160821.htm, Public Domain, https://commons.wikimedia.org/w/index.php?curid=11437959

The FPD is capable of carrying and supporting similar riverine elements.  Its well deck is large enough to carry up to sixteen Small Unit Riverine Craft (SURC), or similar craft.  The vehicle spaces can carry additional boats or boat maintenance and logistics.  Multiple FPDs could carry and support the equivalent of a Marine Small Craft Company (SSCo).
Additionally, the FPD can carry helicopters and UAVs to provide wide area surveillance and rapid movement of troops and material, as well as striking naval and surface targets.  

Humanitarian Relief / Disaster Response (HA/DR)

This is less of a module than just a feature of a ship with large, open spaces; significant payload; aviation and surface connector support; capable C4ISR; small hospital; ability to produce fresh water; and other core capabilities of an amphibious ship.   The FPD could carry small watercraft and divers needed to survey damaged ports, UAVs for imaging disaster areas, helicopters for distributing relief supplies and carrying personnel, modular hospitals that can be offloaded, as well as relief supplies.  Large disasters require huge movements of resources into the area.  The FPD won't excel at that.  But it can be a capable first responder.   


The FPD-150 has the capacity and flexibility of a medium-sized amphibious ship with the combat systems of a guided missile frigate.  It can self-escort, when needed, act as an escort in a larger task force, or form the core of a small task force itself.  It has the combat systems needed to defend itself from air and sea attack, and contributes greatly to Naval Surface Fire Support with its NMLRS system.  With modules it can contribute to ASW, Mine Warfare, Marine forward presence, and HA/DR missions.  

To steal the analogy, the FPD-150 is a Ford F350 to LCS's (or FFG's) Ferrari.  It's big, boxy, roomy, and can carry a load.  It's adaptable to many missions beyond its original specification, just like a pickup truck.


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