October 16, 2019: After seven years of development the U.S. Navy Knifefish UUV (Unmanned Underwater Vehicle) is ready for service. Originally developed for use on the LCS (3,400 ton Littoral Combat Ships) for minesweeping, the Knifefish and the smaller Kingfish and Swordfish are based on commercial Remus 100 and 600 UUVs that were successfully used since 2003 in the Persian Gulf to search for naval mines. The navy militarized the Remus 100 and 600 as Swordfish and Kingfish.

The latest and largest of these UUVs is the Knifefish UUV which is the size of a standard (533mm/21 inch) torpedo. It weighs 770 kg and is 5.8 meters (19 feet) long. This is lighter than an actual torpedo. Knifefish is a militarized version of the Bluefin UUV, which became available about the same time as the smaller and similar Remus UUVs. Since the Bluefin was larger it had more capabilities and was more expensive. As a result, the smaller and simpler Remus UUVs were available for commercial and military use first. The U.S. Navy recognized that the larger Bluefin UUV was easier to militarize than the larger Remus 6000 and would be available sooner. Also, the Remus 6000 was designed mainly for exploring at very deep (6,000 meter) waters. The navy didn’t need that capability for its Knifefish.

The militarized Remus UUVS were collectively called the MK18 UUVs and they had long been used commercially for underwater reconnaissance and survey. They have also been bought by navies to search for mines. The U.S. Navy has been using the smaller (26.4 kg/80 pound) Remus 100s for this in Iraq, and the Remus design is highly regarded by military and commercial users. The navy renamed the Remus 100 the Mk18 Mod 1 Swordfish.

The Mk18 Mod 2 Kingfish is based on the Remus 600 and entered service in 2013. This is a 240 kg (528 pound) UUV that also looks like a small torpedo and is basically a larger version of the Remus 100 (a 37 kg vehicle that is 1.6 meters long and 190mm in diameter). Remus 600 is 3.25 meters (10 feet) long and 320mm in diameter. Carrying a side-scanning sonar, and other sensors, a Remus 600 can stay underwater for more than 24 hours, traveling at a cruising speed of 5.4 kilometers an hour (top speed is nearly twice that). The UUV can operate up to 100 kilometers from its operator and dive to 600 meters (1900 feet). The UUV keeps costs down by using GPS, in addition to the somewhat less accurate INS (inertial guidance system). The UUV surfaces every hour or two to get a GPS fix and then goes back to doing what it was programmed to do. The INS does not need an external signal to know where it is and regularly upgrades its position via the more accurate GPS.

Both Remus models were designed mainly for civilian applications like inspecting underwater facilities, pollution monitoring, and underwater survey or search. The “100” and “600” designations come from the maximum depth (in meters) each vehicle can operate at. Remus 100 entered commercial service in 2001, and the more powerful Remus 600 in 2005. Both were quickly adopted for similar military and police applications, like searching for mines or other terrorist activities. Belgium, Australia, and New Zealand also used Remus 100, and over a hundred are in use. This success led to the development of the larger Remus 600, which is used by Britain and the U.S. Depending on sensors carried, each Remus 600 costs between a million and two million dollars. The Knifefish costs at least 50 percent more than Kingfish but has more capabilities. The LCS ships are carrying two Kinfefish UUVs and a variable number of Mk18s. The navy has found that the Mk18s are easier to use as a rapid-response system. Mk18 teams with several Swordfish and Kingfish UUVs can be flown to anywhere in the world and operate from whatever navy ships are available. This includes 11 meter (35 foot) RIBs (Rigid Inflatable Boats) from which Mk18s can be deployed and recovered.

The Swordfish is used frequently as its main function is to map ocean bottoms to provide baseline data for Kingfish and Knifefish to use to quickly detect where something new, like a naval bottom mine, has been placed. The Knifefish can do this but its batteries have only 16 hours endurance. However, it can be programmed to search a specific area, take pictures of suspicious objects and mark the location. The Knifefish can transmit data in real-time but that requires additional equipment onboard. Knifefish can also detect and avoid floating underwater mines and their tethers (to the bottom) or if they lack tethers, which makes them very dangerous. Knifefish will join Mk18s already working regularly in the Persian Gulf and the Red Sea, two places where Iran has been planting naval mines.

What it comes down to is Swordfish is for constantly surveying coastal ocean bottoms for baseline data while Kingfish searches areas suspected of having mines and Knifefish is an enhanced Kingfish that that can do a more thorough job of detecting and locating all types of mines in an area. The U.S. Navy already has about a hundred of these three UUVs, most of them Swordfish models. More Kingfish and Knifefish UUVs are on order.