Two Birds with One Stone: A New Patrol Craft and Unmanned Surface Vessel

In “The Future Navy,” Admiral John Richardson synthesized two important conclusions from the fleet architecture studies: “First, the nation needs a more powerful Navy, on the order of 350 ships, that includes a combination of manned and unmanned systems. Second, more platforms are necessary but not sufficient. The Navy must also incorporate new technologies and new operational concepts.”¹ He goes on to emphasize that “unmanned systems must also be an integral part of the future fleet” and that they must be “affordable enough to buy . . . in large numbers, and networked in order to expand our presence in key areas.”²

Medium displacement unmanned surface vessels (MDUSVs) are coming to the fleet; but when, how, and what roles they will fill are open questions. Rather than developing a new MDUSV from scratch, the Navy should take advantage of the requirement to replace the Cyclone-class patrol coastal (PC) ships to develop a capable, mature MDUSV—killing two birds with one stone. The U.S. Coast Guard’s Sentinel-class cutter offers an excellent starting point.

The USV Imperative

Each fleet architecture study follows a different operational approach to overcome the challenge of adversary long-range precision fires enabled by persistent intelligence, surveillance, and reconnaissance (ISR). Each produces a distinct fleet architecture to support a larger operational vision, proposing low-cost alternatives, including USVs, to grow and disperse the fleet. The Navy Project Team proposes a large growth in unmanned systems, suggesting a USV based on the 75-ton Mk-VI special operations craft.³ The Center for Strategic and Budgetary Assessments (CSBA) study focuses on patrol vessels, frigates, unmanned underwater vehicles (UUVs), and larger USVs for the bulk of the unmanned system growth, citing the 145-ton Sea Hunter USV as an example.⁴ The MITRE study proposes conventional submarines and magazine ships to grow the fleet, but suggestively confines unmanned systems to a classified appendix.⁵

A ship-design study sponsored by the Chief of Naval Operations’ Surface Warfare Directorate describes a significantly more capable USV than even the Sea Hunter. The proposed 318-ton vessel would carry a hull-mounted sonar, air/surface search radar, soft-kill self-defense system, and a Mk-56 vertical-launch system, while also having a 10,000 nautical mile-range and 60-day endurance.⁶ Similarly, the Strategic Capabilities Office, in coordination with the Navy’s Unmanned Maritime Systems Office, explored the availability of a USV with a 4,500 nautical mile-range, 30-day endurance, 27-knot top speed, redundant propulsion, and 20 tons of mission payload.⁷

These five studies reflect the broad consensus that MDUSVs will eventually bring great capabilities to the fleet. But how to get there?

The USV Challenge

A 2013 RAND study found that USVs should have autonomy, assured communications, modular payloads in common platforms, optional manning to mitigate autonomy challenges, and very long endurance.⁸ However, the technology, platforms, and operating concepts for each key unmanned capability have yet to mature.

Looking back at 20 years of Navy shipbuilding shows that ambitious new technology takes time to mature and still more time to integrate. The future MDUSV will undoubtedly require extensive developmental testing and evaluation to mature the overall system while also integrating its capabilities into the fleet. To minimize programmatic risk, the next MDUSV should evolve an existing manned platform rather than starting from a clean-sheet design. Long before the Navy trusts an autonomous MDUSV to navigate a crowded international strait under challenging conditions, it must provide the system’s artificial intelligence (AI) with the data from thousands of supervised evolutions—all the more reason to field a mature platform sooner.

There are other challenges beyond autonomy. The first casualty of critical equipment should happen with an engineer on board, not thousands of miles into an unmanned mission. An MDUSV developed from an existing manned platform will ensure this level of supervision and reduce technical risk, allowing the Navy to incrementally reduce the crew size as the unmanned system components mature.

Fitting the MDUSV into the Future Fleet Design

As the prevailing concept for fleet operations shifts from defense-in-depth, centered on the aircraft carrier, to network-centric distributed maritime operations, the network will become the new high-value unit, the fleet’s center of gravity. A reliable battle network is already essential for winning a modern fleet engagement, but scattering the units with the hope of complicating the enemy’s targeting has the unfortunate side effect of making the network both more vulnerable and more valuable.  

In a recent interview, Bryan McGrath, one of the CSBA study’s authors, expressed satisfaction with the weapons that support increased lethality, while lamenting “the networking, the ISR, and the connective tissue among all the elements,” adding, “What we don’t have is all the interstitial stuff that helps tie it all together.”⁹ In his June 2017 Proceedings article, “Think Outside the Hull,” Captain Robert Rubel makes a similar argument, writing, “The immediate need is to create a robust and resilient battle force network.”¹⁰

MDUSVs and their manned precursor vessels could hold the network together for the rest of the fleet in a communications-degraded environment. The DARPA towed-airborne lift of naval systems (TALONS) project, recently tested on board the USS Zephyr (PC-8) and the Sea Hunter, can elevate a 150-lb datalink pod to 1,500 feet and keep it there for weeks, expanding the payload’s effective radar horizon to more than 50 nautical miles.¹¹ An elevated data-link pod could maintain the common operational picture within a dispersed surface action group by using a burst-transmit, low-probability-of-detection waveform, switching to a higher fidelity mode for weapons employment.

Although supporting the fleet’s network and sensors should be the initial focus, MDUSVs with the appropriate payload would be capable of performing many other important missions, including antisurface warfare, antisubmarine warfare, mine countermeasures, and convoy escort. The single most critical platform attribute for this sort of modular flexibility is payload capacity. Intuitively, displacement determines payload capacity—a 75-ton Mk-VI-based MDUSV would have a smaller payload capacity than the 145-ton Sea Hunter, which would have a far smaller payload capacity than a 350-ton, PC-derived MDUSV. Nothing is free, and this larger USV would cost roughly three times as much as a Mk-VI and twice as much as a Sea Hunter. That greater cost would buy more than just payload capacity, however. Unlike the Mk-VI, a larger USV would enjoy significant range and endurance and the ability to self-deploy from the U.S. And unlike the Sea Hunter, it could embark a small crew as certain missions might require.

Converging Requirements

The Cyclone-class PC will reach 30 years of service life starting in 2023, despite originally having a designed service life of 15 years. Though the littoral combat ship (LCS) was intended to replace patrol craft, mine countermeasure ships, and frigates, the program’s truncation to 33 hulls will likely force the Navy leave important missions unresourced when the PCs retire. Furthermore, replacing the Cyclone-class with an LCS costing more than 10 times as much is no way to grow and disperse the fleet.¹² Combine these considerations with the still higher cost and capabilities of the FFG(X) program, and it becomes clear the Navy needs a replacement PC, or PC(R), that could quickly and cheaply supplement the lower end of the fleet architecture.  

Fortunately, a mature, non-developmental option for this PC(R) already exists. The Coast Guard acquired the first 154-foot, 353-ton Sentinel-class fast response cutter (WPC) in 2012 to replace the aging, 110-foot Island-class cutters. The WPC is substantially similar to the existing Cyclone-class. The Coast Guard has already commissioned 29 of the planned 58 hulls, with the final delivery planned for 2024. The overall program cost averages $58M per cutter, though the six vessels funded in the FY17 budget averaged $54M.¹³

A Roadmap for MDUSVs

The Navy should latch onto the Coast Guard’s WPC program to acquire a PC(R) that could also serve as a MDUSV development platform and, eventually, a MDUSV. In keeping with the Chief of Naval Operations’ guidance in The Future Navy, this acquisition strategy would evolve an established design on an active production line. A vessel based on the WPC would take advantage of the Coast Guard’s sunk development costs and production learning curve, while also leveraging multiyear procurement to achieve still greater cost savings.¹⁴

Block 1 vessels, incorporating limited designed changes from the WPC, would replace the Cyclone-class at the end of their service lives and serve as technology testbeds for unmanned system components. The transfer of equipment from the retiring vessels would further reduce acquisition costs. Initially, the PC(R)s would fulfill an operational role similar to the Cyclone-class before gradually expanding to other roles. However these vessels might be employed, they would gather important operational data and lessons to incorporate into the MDUSV version.

Block 2 vessels would incorporate proven components of the unmanned systems as they mature in Block 1 vessels. These increasingly automated vessels would exchange some of the space and weight incurred by a larger crew for payload and fuel. The interim design would further mature the unmanned technology while freeing the crew from bridge and engineering watches, letting them focus instead on developing tactics for the MDUSV. This spiral development model would evolve a conventionally manned PC(R) into a truly minimally-manned vessel—but only after the enabling technology had proven reliable.

Block 3 vessels would be operational USVs, with some optionally manned vessels embarking teams for specific missions, such as maritime interdiction, training, or rapid on-site weapons release authority, while leaving other vessels completely unmanned to perform the dirty, dull, or dangerous missions for which a crew is a liability rather than an asset. This vessel could use the same hull as the PC(R), or leverage the proven systems in a more capable, purpose-built platform.

Developing a MDUSV from scratch will be costly and take many years. Leveraging an existing Coast Guard platform to both replace the Cyclone-class PC and develop a MDUSV is a realistic and innovative approach that the Navy can not only afford, but needs in the face of many other warfighting and shipbuilding priorities.