In 2013, when I first heard that the Navy was developing an Anti-Torpedo Torpedo, I had hopes it might be the basis for a ship stopping system for the Coast Guard. In 2019, we learned that the systems which had been deployed on five of the Navy’s aircraft carriers were being removed. It seemed the program was dead. In fact, it appears very much alive, and apparently the Navy has targets other that adversary torpedoes in mind. If the Coast Guard is ever to have this weapon it may be important to understand what the Navy might see in the system.

Northrop-Grumman press release quoted in part:

Northrop Grumman has successfully manufactured and tested the first industry-built Very Lightweight Torpedo (VLWT) for the U.S. Navy. The prototype torpedo is based on the Pennsylvania State University Applied Research Laboratory’s (PSU-ARL) design that was distributed to defense industrial manufacturers in 2016. Northrop Grumman, which independently funded the research and development, will offer the design-for-affordability improvements to this VLWT as Northrop Grumman’s response for the Navy’s Compact Rapid Attack Weapon program.

Applying its engineering and manufacturing expertise, Northrop Grumman improved upon the VLWT baseline design to replace high-cost components and drive overall affordability, reproducibility and reliability. Those altered sections were built and tested using PSU-ARL’s own test equipment for confidence.

“The successful testing of the torpedo nose on the first try is a testament to Northrop Grumman’s design-for-affordability approach, which will significantly reduce cost without sacrificing operational performance,” said David Portner, lead torpedo program manager, undersea systems, Northrop Grumman.

TheDrive dug into this a bit further and found the supporting FY2021 budget line items  and justification under the name Compact Rapid Attack Weapon (CRAW), significantly it is a program of record.

The thing I find interesting is, this is touted a multi-platform, multi-mission weapon. The primary capability being talked about is as a hard kill anti-torpedo weapon, but apparently it is a modular weapon that may be reconfigured for different missions.

There is more information in an earlier TheDrive article.

These weapons could offer added offensive firepower, as well as an all-new anti-torpedo defense interceptor capability. The mini-torpedoes use a common body and future variants might also arm unmanned ships or submarines, as well as flying drones, act as naval mines, and more.

The Common Very Light Weight Torpedo design that the weapon is based upon is reportedly 6.75″ in diameter, about 85″ in length, and weighs about 220 pounds (100 kilos). If it is truly modular its length and weight may vary somewhat. It might be possible to make a version with an enlarged warhead.

The familiar Mk46 light weight torpedo is more than twice as large. The newer Mk 50 and Mk54 torpedoes are similarly sized.

• Length: 8 ft 6 in (2.59 m), 102 in
• Weight: 508 lb (230 kg) (warshot configuration)
• Diameter: 12.75 in (323.8 mm)
• Range: 12,000 yd (10,973 m)
• Warhead: 96.8 lb (43.9 kg)

The Navy’s standard heavy weight torpedo, the Mk48, is 16 times larger than the Common Very Light Weight Torpedo design.

• Length: 19 feet (5.8 meter) or 228 in
• Weight: 3,695 lb (1,676 kg) (ADCAP)
• Diameter: 21 in

Advantages of small size: Small size can convey several advantages.

• More weapons
• Smaller cross section
• Lower noise
• Use by smaller platforms

A smaller weapon allows a greater number of weapons in a given magazine space. Space for torpedoes on submarines is limited and the Mk48 costs $10M each, so there are good reasons not use too many on one target or to use them on small targets . The VLWT could be used to swarm larger targets or individually against small craft including unmanned surface and subsurface vessels. As a rough estimate it looks like about 14 of these smaller weapons could fit in the space currently required for one Mk48 torpedo.

A helicopter could probably carry at least twice as many VLWT compared to the current light weight torpedoes. 

The frontal area of a 6.75″ torpedo is only 10.3% that of a 21″ torpedo meaning that it would be harder to detect using active sonar.

The power required to propel such a small torpedo is significantly less that that of a 21″ torpedo. Consequently it should put much less noise in the water, making it harder to detect by passive means

Being harder to detect means these weapons could probably get closer to a target before it becomes aware it is under attack.

Light weight and small size also means these weapons might be deployed from platforms that currently cannot support heavier weapons. These might include the Common Unmanned Surface Vehicle (CUSV) or the MQ-8C Fire Scout drone helicopter. It might also arm the MQ-4C Triton.

Parallels from above water missiles: What we are seeing here has parallels to what has already happened in the field of guided missiles above water.

• Smaller but more numerous missiles
• Simultaneous or closely sequenced attack
• Multi-Packed missiles
• Anti-Radiation missiles

The Russian Navy is putting smaller missile on their ships but in greater numbers. We see them moving from four very large missiles to 16 smaller missile. It is perhaps less obvious, in the US Navy, but they are using the smaller Naval Strike Missile in applications where they would previously used the larger Harpoon missile, and it appears the new frigate will be equipped to carry 16 of these. The reasoning is understandable. With increasingly robust anti-missile defenses, there is a need to swam the defenses with numerous missiles arriving simultaneously or in closely sequenced attacks. As torpedo countermeasures become more effective there may be a similar move to launch a swarm of smaller torpedoes.

We have begun to see more than one missile housed in a single VLS. The Evolved Sea Sparrow Missile (ESSM) is commonly packed four to a canister in Mk41 VLS and the larger launch tubes like the Virginia Payload Module may house even more missile in a single tube. Similarly, it appears that it might be possible to use a canister to launch as many as seven of the VLWT from a single torpedo tube without the need to reload.

Since at least the Vietnam war, we have seen anti-radiation missiles used to attack sensors controlling countermeasures systems including missile control radars. We may see the use of VLWT to attack active sonar systems that might cue torpedo countermeasures prior to arrival of a larger torpedo.

Submarine Attack on Surface Ship Scenario:

VLWT might be used as follows to attack a surface combatant.

The enemy vessel is, for the scenario, a Project 22350 Admiral Gorshkov class frigate with both hull mounted and towed active/passive sonars, a towed torpedo decoy system, and a PAKET-NK hard-kill anti-torpedo defense system.

The US submarine launches seven VLWT and a single Mk48 torpedo in a sequenced attack. The VLWT are launched first to arrive earlier than the Mk48. The first VLWT sacrificially destroys the towed decoy. The remaining six target first the active sonar sources and then the ship itself. With six targets inbound, the PAKET-NK hard kill system has only four ready rounds. If it works perfectly, it will destroy four of the six remaining VLWT, but the other two will destroy the two active sonars including the one in the bow. When the Mk48 arrives it will have no distractions to deal with and will detonate under the frigate, breaking its back.

For the Coast Guard:

It appears these Very Light Weight Torpedoes may be adequate for what I see as the Coast Guard’s requirement to be able to forcibly stop any vessel regardless of its size. It would need to be able to target the ships propellers, but this has been possible since WWII. Given their size and weight, and apparently relatively low cost, even WPCs and WPBs should be able to carry more than one or two to provide redundancy.