Complex sentence: However, Halsey ordered the rest of the cruisers to leave "Chicago" behind and head for port at Efate, in the New Hebrides, which they did at 15:00, leaving behind six destroyers to protect "Chicago" and "Navajo".
Split into simpler sentences: However, Halsey ordered the other cruisers to leave "Chicago" behind and head for Efate in the New Hebrides. They left which they did at 15:00, leaving behind six destroyers to protect "Chicago" and "Navajo".