This may seem an unusually upbeat poem for MacNeice – at times you feel all it needs is a mention of the happy isles and the great Achilles to segue into Tennyson’s ‘Ulysses’ – but of course there is a good deal of tension here between the apparent negativity of the remembered past and the positivity of aspiration for the future. Did MacNeice see himself as one of Auden’s ‘ruined boys’, forced to seek redemption? But I am drawn to its valiant spirit, even if that spirit is undercut by a slight desperation.
Thalassa
Run out the boat, my broken comrades;
Let the old seaweed crack, the surge
Burgeon oblivious of the last
Embarkation of feckless men,
Let every adverse force converge –
Here we must needs embark again.
Run up the sail, my heartsick comrades;
Let each horizon tilt and lurch –
You know the worst: your wills are fickle,
Your values blurred, your hearts impure
And your past life a ruined church –
But let your poison be your cure.
Put out to sea, ignoble comrades,
Whose records shall be noble yet;
Butting through scarps of moving marble
The narwhal dares us to be free;
By a high star our course is set,
Our end is Life. Put out to sea.
Louis MacNeice
David Sutton 
Good one. Did not know this poem; great many thanks.
“Thalassa” (or “Thalatta”) is a Greek word for “sea”. The title, I feel sure, must be an allusion to a famous scene from Xenophon’s Anabasis, which every schoolboy read back in MacNeice’s day, back when MacNeice was a tutor and schoolboys actually studied Greek.
Xenophon was part of a Greek mercenary force which fought against the Persians in Asia Minor. They were beaten, and fled north toward the Black Sea, with the Persians carving them up from behind. At last, in despair, they came to a crest and looked down and saw the sea. They broke ranks, abandoned their plunder, and ran down the hill embracing each other, shouting, “Thalatta! Thalatta!” Xenophon, Anabasis, IV.7.24.
Yes indeed, thank you, I forgot it might be necessary to explain the title in these benighted days!