Pretty close, but only the *Little Boy* unit dropped on Nagasaki utilized Plutonium. The Little Boy unit dropped three days previously on Hiroshima was a gun-type fission unit that used Uranium U-235.
Even more interesting: the German *Virus House* design, which used U-235/U238 in layers, shielded by nothing more than kerosene. The bottom half of the unit was a massive iron semisphere, which when it impacted with the Earth at near supersonic speed, crushed the plates together and sprayed the kerosene out from between them, allowing the mass to go critical. Would it have worked? I'm glad we never found out.
