|Manufacturer||Galtor Naval Yards|
|Mission||Main Battle (Blue Water)|
|Armor||14.5 SeaSlab Standard|
|Engine||270 Doorman Naval HyPerOx I.C.E.|
The Neptune submarine, put into service by Galtor Naval Yards in 2950, was designed by House Davion as a means to defend their underwater command posts from enemy attacks, after they had adopted the strategy to build fixed command posts underwater to protect the vital installations from orbital or aerospace bombardment. This also protected them from most ground units, as even BattleMechs operate at limited efficiency underwater. The Neptune proved effective in this role during the 4th Succession War, and was a common defensive unit on Federated Suns (and later Federated Commonwealth) worlds with aquatic installations. After Galtor's conquest by House Kurita during the 4th Succession War, the Draconis Combine began to deploy the Neptune on their worlds as well.
The Neptune utilizes a double hull design, rated for a depth of up to one kilometer, with the outer hull mounting fourteen and a half tons of armor protection. Despite its small crew, conditions on the Neptune are cramped due to the bulk and complexity of its machinery. The Neptune's Doorman Naval ICE is a diesel design, operating as a normal engine on the surface (or up to twelve meters using a snorkel system) but able to burn a mix of diesel and hydrogen peroxide underwater. Its periscope also extends to a height of twelve meters.
Being a submarine, the Neptune is primarily armed with torpedo systems, navalized versions of proven missile launchers. For long range firepower, it mounts a Sea Devastator LRT-20 Long Range Torpedo system with twenty tubes, though it only has enough ammunition to fire six volleys. Twin Sea Harvester SRT-6 Short Range Torpedo systems provide close range firepower, again with only a single ton of ammunition between them. As a backup weapon, or for use in attacking land targets, the Neptune also mounts a single Sutel XII Large Laser.
- LRT - Designed to counter an issue with limited reloads, the LRT variant of the Neptune replaces the Sutel XII with another Sea Devastator LRT-20 launcher and three additional tons of ammunition.
- SRM - Similar to the LRT variant, the SRM variant also removed the Sutel XII to make room for three additional Sea Harvesters and increased ammo for both sets of launchers. BV (2.0) = 1,075
- Hunter-Killer - This version introduced in 3024 drops the laser and reconfigures the torpedo launchers. In the front it mounts four SRT-6s with three tons of ammunition between them and one LRT-15 with two tons of ammunition. A LRT-5 and a SRT-4, with one ton of ammunition each, were added to the rear. The vessel's armor was reduced by two tons, although the rear armor was actually improved over the basic version. BV (2.0) = 948
- Hyper - This experimental version combined a standard Neptune chassis with a hydrofoil system. The DCMS experimented with using the hydrofoil system as a rapid deployment system for the submarine. When it reached a combat zone, it would then retract the hydrofoil and operate as a conventional submarine. By removing the large laser, power amplifier, and a half ton of armor, designers were able to install the hydrofoil, the hydrofoil control system, an additional SRT-6 to cover the aft, and an extra ton of LRT ammunition. During the only test, the Neptune Hyper was able to operate as a submarine, but the hydrofoil system snapped off the hull and sank the craft. The hydrofoil system couldn't stand up to the pressures at depth, and the DCMS cancelled the project.
 Named Vessels
- FSS Ward - The Federated Suns Ship Ward was a Hunter-Killer variant of the Neptune which served during Kurita's Galtor campaign of 3025. The ship was the lead vessel of a "Wolfpack" of four other Neptune Submarines. On May 18th, the Ward engaged Kurita 'Mechs in the water, making their way to Galtor's underwater planetary command base off the coast of New Derry. The Ward itself managed to destroy a Kurita Jenner. However, the 'Mechs were decoys for incredibly fast commando submarines. Later found out to be called Koryu. The ships sped past the Ward's Wolfpack and managed to deliver its payload of DEST Commandos to the Davion base. Unfortunately, the Ward and her near-sister ships were too slow to attack them in time. After the destruction of the Command base, the Ward and its Wolfpack were reassigned to patrol the coast of Eire for the rest of the campaign.
 Design Quirks
- Difficult to Maintain
- Illegal (Dual Motive System)
- Nonfunctional (Hydrofoil Motive System)
- ↑ Combat Operations, p. 126
- ↑ Technical Readout: 3039, p. 99
- ↑ 3.0 3.1 3.2 Technical Readout: 3026, pp. 82-83, "Neptune Submarine Profile"
- ↑ 4.0 4.1 4.2 Technical Readout: 3026 Revised, pp. 86-87, "Neptune Submarine Profile"
- ↑ 5.0 5.1 5.2 5.3 5.4 Technical Readout: 3039, p. 98
- ↑ Record Sheets: 3039, p. 56
- ↑ Record Sheets: 3039, p. 57
- ↑ Historical Turning Points: Galtor, p. 19
- ↑ 9.0 9.1 Experimental Technical Readout: Boondoggles, p. 10
- ↑ Historical Turning Points: Galtor pp. 1, 9 - In the Deep (story) & Enemy Below (Scenario) - Story of the F.S.S. Ward and its actions during Galtor campaign.