What battles were initially complete disasters for Rome?
The first few naval battles were disasters for Rome. However, after training more sailors and inventing a grappling engine, a Roman naval force was able to defeat a Carthaginian fleet, and further naval victories followed. The Carthaginians then hired Xanthippus of Carthage, a Spartan mercenary general, to reorganise and lead their army. He cut off the Roman army from its base by re-establishing Carthaginian naval supremacy. The Romans then again defeated the Carthaginians in naval battle at the Battle of the Aegates Islands and left Carthage with neither a fleet nor sufficient coin to raise one. For a maritime power the loss of their access to the Mediterranean stung financially and psychologically, and the Carthaginians sued for peace.