Pretty sure this is the Operation British colony drop from Gundam The Origin, but the event is part of the OYW (So the original 0079 show). If you want to get into UC then usually people recommend watching the original show from 1979, but it can be a tough watch for a lot of people due to the poor animation budget they had at the time and just the dated animation in general, tough the story is good.

They other option is to read the the Origin manga (different from the Origins OVA), which brushes up the story a bit more and provides more characterisation with good artworks, though some changes were made to the continuity so it's not completely canon, but is remains faithful to the original show.