alternatehistory.com

3 May

The second attack on Presque Isle bay begins. Libra, Scorpio, Pisces and Capricorn are present, along with a trio of gunboats (the Mackerel, Magpie and Ripple) as a second line for bombardment purposes.
Their arrival so soon after the first - failed - attack is a cause for some consternation, though fortunately the week's time has let the Union shipwrights work around the clock and complete the two modified Casco class monitors.
These two ships - Suncook and Tunixis - are much reduced from the original Casco plans, and in the process of reducing them down to a smaller size of vessel it was noticed that they would not have any bouyancy under combat load. As such, these ships of what will become known as the Suncook class do not share the problem which would have befallen the Cascos if any had been completed - they are, in fact, able to float.
Both vessels have lighter side armour than the original Monitor and are shallower in draft, though mounting similar guns - Tunixis mounts one 11" Dahlgren and one 8" Parrott, while Suncook has a pair of Dahlgrens sleeved down to about 9" and rifled.
Their armour is similar to that of the Monitor as well, though a mild alteration has been essayed in that the 1" plates are separated by thin laminates of wood to absorb shock. It was in adding these that the original bouyancy calculations were redone, and the problem discovered - to whit, the original Casco were designed assuming 15/16" plates and seasoned wood, and ordered with 1" plates and greenwood.

The Zodiacs open their broadsides and begin shelling the Union earthworks at about 3pm. This cannonade goes on for about an hour, with the gunboats moving in to find good arcs, and at the end of this time the fortifications - not fully repaired from last week - are essentially wrecked, no longer able to offer meaningful resistance.
While this is going on, Suncook and Tunixis move to the shallow bar of the bay and begin firing on the British ships, using their relatively long range (for monitor-type ships) to reload and fire with some of the gun crews outside the armour box. This speeds things considerably, and over the next hour Libra takes several hits and the Magpie loses her 68-lber main gun to a 9" ball. The sleeved 9" guns are proving reasonably effective - at this range they are causing some concussion, and are being more accurate than the previous guns the Union was using - but full charges are not being used yet, as there is a considerable risk associated.
At about ten past four, the British ironclads move in. After the problems of last week, they now move en echelon - with the gunboats forming a second angled line behind them, ready to react. The Union ships move to counter them, with both Suncooks ordering their crews back behind the armour, and there is something of a lull, as it takes about a quarter hour for the British squadron to get to battle range and the Union gunners are not willing to risk firing off their readied artillery (fifteen minutes is the reload time for the 11" gun).

A few minutes before 4:30, the engagement moves into a final phase. Mines are detonated in the bar, sending up two plumes of dirty water but missing all the British ironclads (as before only a few of the devices were able to endure their time underwater) and the Union formation moves in.
It quickly dissolves into a melee, with the Zodiacs running out their loaded guns from behind armour shutters for just long enough to fire on visible targets, and the Suncooks trying to get the much-coveted direct hit they require. Over the course of the battle the Mackerel is hit hard by shellfire and left disabled, while the Scorpio takes a penetration which disables two guns (via a heavily overloaded 9" gun which fired successfully) and Libra loses her smokestack which renders her unable to move. The Pisces and Capricorn both take more minor damage, including the effects of a shell shooting away the bowsprit on the Pisces.
The Union ships are in serious trouble, however. Between them the British ships carry 33 68-lber high velocity guns and sixteen 110-lber rifles, along with a few lighter guns on the gunboats, and this concentration of fire renders the wooden ships hors d' combat before battering through the turrets of Suncook and Tunixis to force them to strike.

Battered but triumphant, Yelverton (flying his flag in the Capricorn) demands the surrender of the dockyards. This is met with stonewalling and silence, and ultimately he simply has his ironclads shell the fitting-out docks, slips and other shipbuilding equipment - thus destroying the Union's main naval construction centre on the Great Lakes at a stroke.
This task done, his flotilla puts hot shot into the grounded American vessels (Hunter and Chippeway) to destroy them, and leaves for Windsor.