Board Thread:Questions and Answers/@comment-92.26.10.25-20131103085357/@comment-84.25.233.211-20131121122139

For the upgrade you must at least have the Hull researched in the naval lab or you must have that hull as a price during raids or missions. If not yet researched or not got it, then retrofit lab will show you all the retrofit lab can upgrade, but you can't upgrade them.