>> From my college days I remember learning that DC was not
>> good at long distance transmission.
>> Yet, Britain and Ireland are transmitting DC across the
>> Channel.
For overhead transmission lines, yes there are issues with DC such as corona discharge.
But for underwater transmission there is another huge issue which makes AC less practical - the large capacitance of the underdwater cable.
You can just tune that out...a few ferrite rings will soon take care of it.