The Middle-Son 1999 is a submarine from the Regular Army to scouts the water areas or offesive ways.
The Middle-Son 1999 is an upgraded version of the old Middle-Son 1986. Only one unit of it was ever produced, but it disappeared mysteriously, and nobody really knew why. During the First Modern War, the wreckage of the Middle-Son was found in a dried-up riverbed in the Villeneuve Mt. System, but nobody knows how it ended up there. As it stays there, the Rebel Army uses it as a shelter or interceptor.
- It resembles an Ohio-class submarine
- It's probably the current main submarine class for the Regular Army.
|Mechanized||SV-001 (Metal Slug) | SV-001 Type-R | Slug Copter | Slug Flyer | Slug Sub | Astro Slug | Slug Gunner | Slugnoid | LV Armor | Walking Machine | Slug Mariner | Drill Slug | M-15A Bradley | Metal Claw | Forklift | Slug Mobile | Augensterm | Protogunner | Slug Digger | Slug Trolley | Slug Armor | Slug Gigant | Golden Slug | MS-Alice | Ball Slug|
|Animal||SV-Camel | Elephant Slug | Ostrich Slug | Donkey Slug|
|Other||Middle-Son 1986 | Middle-Son 1999 | SV-002 | Borobune Slug | Motorcycle | Regular Army Helicopter | Landseek | PA33-21 Boat | RA-TTT | Rootmars|