TFTD, with alien colony on the globe
1. remove all harpoons and harpoon clips from the craft and stores, keep only 1 of each
2. take both on the alien colony mission
3. throw the loaded harpoon out from the Triton on the ground (will be recovered if you win a mission)
4. go to green exit area and abort stage 1
5. kill all aliens in stage 2 (i.e. win the mission)
In Debriefing, you'll see 1 extra harpoon clip in LOOT.
In the base, you'll see 1 harpoon + 2 clips (instead of 1 harpoon + 1 clip).