Chaos in Italy

[OFSO]

As I thought, the marines were carried on board to deal with the bolshi crew:

Historically, tasks undertaken by marines have included: helping maintain discipline and order aboard the ship (reflecting the pressed nature of the ships' company and the risk of mutiny), the boarding of vessels during combat or capture of prize ships, and providing manpower for raiding ashore in support of the naval objectives.

However that last item would indicate their usefulness in dealing with immigrants waiting to sail to Europe.