How Axis forces might attack Habakkuk

How could Axis naval and air forces counter or destroy Habakkuk?

Only through a massed submarine or air attack aimed at cracking, melting, or disabling the vast escorted sea base.

A single submarine would likely exhaust its torpedoes before sinking Habakkuk. Attackers would need a wolf pack or a very large air strike concentrated on the same area. Heating and fracturing the pykrete or making the base uninhabitable might work better than seeking an ordinary ship kill. The structure could also support its own escorts at wharves along its sides, complicating any approach. Defeating it would therefore require a campaign against a defended sea base rather than one successful hit.