Was this ever discussed in any episode, or as a side-plot somewhere?
It's not Earth's army, it's Democratic Order Of Planets military. Better known as D.O.O.P. Which Amphibios 9 is a member (Kif's home planet).
"DOOP? What's that?" ―Fry
"It's similar to the United Nations from your time, Fry." ―Professor Farnsworth
"Or like the Federation from your Star Trek program." ―Hermes
DOOP has a large military force that polices the space of its member states. Among its assets are a large number of soldiers and a fleet of ships, which are used to defend its members from attack and to defeat their enemies. The flagship of the fleet, the Nimbus, commanded by Zapp Brannigan, is stationed on Earth, though it often travels to other places in the universe during the course of its duties.
Known DOOP Personnel Edit
- Zapp Brannigan: 25-Star General, Captain of The Nimbus
- Lieutenant Kif Kroker: First Officer on The Nimbus, Personal Assistant of Zapp Brannigan.