Why Aboukir, Cressy, and Hogue were exposed

Were Aboukir, Cressy, and Hogue at sea mainly to give reservists experience rather than for a tactical need?

No. They were in the wrong place at the wrong time rather than primarily deployed as a sea-training exercise.

The three cruisers were at sea because of their operational assignment rather than a requirement to give reserve crews experience. They were performing a duty in a location that exposed them to submarine attack. The explanation keeps the focus on deployment and escort scarcity rather than presenting the loss as a deliberate training risk.