It is a long time since I used the IXD2, but if I remember correctly if you start the campaign with the IXD2 (upgrading from the type VII or IX B-C), the FIRST time you'll leave for the mission you WILL NOT get the "sonar destroyed" message.
But if, during that first patrol with the IXD2, you'll get some damage (from dc charges or aircraft), at the beginning of the NEXT patrol you'll get, while still in port, the "sonar destroyed" message.
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