Open source information indicates that USNS Pililaau (T-AKR-404) was recently - perhaps still is - moored at Diego Garcia. This is a MSC Large RORO vessel of the Bob Hope class designed to move heavy military equipment. Other vessels of the same class appear to be in US ports.
There are many storage sheds on Diego Garcia.
Typically the class can carry up to 60 tanks and 1000 trucks plus a shedful or two of containers.