What makes this ship so special (according to Holmes)?

Excerpt: Old Ironsides
by Oliver Wendell Holmes

Ay, tear her tattered ensign1 down! Long has it waved on high,
And many an eye has danced to see That banner in the sky;
Beneath it rung the battle shout, And burst the cannon's roar; The meteor of the ocean air Shall sweep the clouds no more!

Her deck, once red with heroes' blood, Where knelt the vanquished foe,
When winds were hurrying o'er the flood And waves were white below,
No more shall feel the victor's tread, Or know the conquered knee;
The harpies2 of the shore shall pluck The eagle of the sea!