Table:
text: List of grenade launchers
Rocket Propelled
Rocket Propelled
Name_designation Year_of_intro Country_of_origin Primary_cartridge Type_
M1 Bazooka 1942 United States 60mm Recoilless
M2GC 1948 Sweden 84mm Recoilless
Northover Projector 1940 United Kingdom 63.5mm Recoilless
Panzerfaust 1943 Germany 150mm Recoilless
PIAT 1942 United Kingdom 86mm Spigot mortar
Rifleman`s Assault Weapon 1977 United States 140mm Close support rocket
RPG-2 1949 Soviet Union 40mm Reusable
RPG-7 1961 Soviet Union 40mm Reusable
RPG-16 1970 Soviet Union 58.3mm Reusable
RPG-18 1972 Soviet Union 64mm Disposable
RPG-22 1985 Soviet Union 72.5mm Disposable
RPG-26 1985 Soviet Union 72.5mm Disposable
RPG-27 1989 Soviet Union 105mm Disposable
RPG-28 2007 Russia 125mm Disposable
RPG-29 1989 Soviet Union 40mm Reusable
RPG-30 2008 Russia 105mm Disposable

Question: What is the country of origin if the year of introduction is 1977 for the grenade launcher list?