And the spark struck out that steed, in his flight (78)
Wrapped in Silence so deep and still (43)
The somerset, British man-of-war; A phantom ship, with each mast spar (19-20)
The alliteration here is "spark, struck" which uses the repetition of the letter "s" at the beginning of the words.
Across the moon like a prison bar (21)
This is personifying the people who are dead by saying they are wrapped in silence when you cannot actually be wrapped in silence
And a huge black hulk, that was magnafied by its own reflection in the tide (22-23)
This metaphor is comparing a phantom ship with the British by saying that they are very much like a phantom ship because they are sneaking into the harbor late at night
Now he patted his horse's side, Now he gazed at the landscape far and near (59-60)
This simile compares the mast of a ship to a prison bar. This is a simile because it uses the word like in the phrase when describing the prison bar across the moon.
This example of allusion if referencing hulk as describing the ships as big and frightening looking as they are coming towards the shore. The poet does this to emphasize how large and dark these boats look in the night.
This is an example of repetition because the poet uses the phrase "Now he.....". This is an example of repetition because he is repeating the same phrase in two lines of the poem that are right next to each other.