alternatehistory.com

8 April
James B. Eads is contracted to build some small ironclads upriver of Baltimore, with the intent being to open the Chesapeake and ideally to sail up the Potomac and sink the Virginia. Eads has a number of ideas, though is dismayed when he starts calculating the required protection - the failure of the Monitor to successfully resist British shot means that either extremely thick layering or a single plate beyond the current capacity of the Union will likely be required. (There is a rolling mill in America which can produce 2" rolled plate, but it is in Richmond.) The alternative is to create hammered plates exceeding five inches, and this is likely to take many months.
He is promised either 15" Rodman guns or 8" (or even 10" once designed) Parrott guns, though he also has an idea about sleeving an 11" Dahlgren down to around nine inches and rifling it and will raise this with Dahlgren as soon as possible.
After much though, Eads decides to compromise with hammered 3" plates and layer them.


11 April
Breakup at the St Lawrence occurs at Quebec. The news is communicated to Cape Breton, and the Aetna makes for the river mouth.
At about this time the Leo, Sagittarius and Capricorn - all under tow - are passing the longitude of Greenland.


12 April
The railroad north from DC is cut. The supplies and munitions in the city are effectively all it has.
For this reason, McClellan determines to cut away from his supply lines in order to get out of the encirclement. This increases the supplies available in the city, and will also let his men move faster and across country (relatively speaking).
Arguments take place over how many troops he should take, and in the end all the soldiers who had been running his supply chain are left in the city. He will recruit more from Pennsylvania and NY, though this will mean contemplating the considerable risk of unarmed supply chain soldiers.

15 April
Aetna passes Quebec. Also on this date, the Welland canal opens for the year.

16 April
The hastily armed screw steamer the Buffalo (formerly the Bay State) attacks Fort Henry, attempting to make her way into Kingston. The old fort is quite decrepit, but serves as a workable base for the entire armament of the HMS St Lawrence (of the War of 1812, now a pier). Around sixty 32-lber guns defend Kingston, as well as smaller weapons, and the Buffalo finds the attack hard going as her own guns are not heavy or numerous enough to do the same thing to the fort which British rifled breechloaders did to US forts.
The battle lasts around half an hour, after which the Buffalo withdraws.