When was Phillip's ship torpedoed?

The short answer is that the S.S. Hato was torpedoed on April 6th, 1942. But we can actually answer this question in a few different ways:

First, in terms of the plot of the novel, Phillip's ship being torpedoed happens in the beginning of the rising action. That is, after the exposition, in which we saw how Phillip and his family lived on Curacao during the war, the rising action begins as Phillip and his mother board the ship to try to escape to the safety of Virginia. That's when the ship gets torpedoed, leading to the rest of the action of the story.

Second, in terms of where in the book we'll find this event, Phillip's ship being torpedoed happens in the first paragraph of Chapter 3.

And lastly, just in relation to the natural timeline of history, although this story is fictional, Phillip's ship being torpedoed happens very early the morning of April 6th, 1942. You can find this information at the very beginning of Chapter 3.