alternatehistory.com

25 April
Afternoon

Over the next few hours, a complicated retreat takes place towards the east. Around four thousand Union troops are captured, though the majority of the Union assaulting troops actually make it across the Niagara river and back to the United States.
Their guns are all captured, but the British commander does not press his advantage - fearing that the same will happen to him in turn if he attempts a major advance.

He is initially praised for his defence of the Welland canal, but as the details of the battle become clear this turns to a very mixed opinion. His tactics are decried as passive, and the possible great victory that could have been won is seen as lost. It is considered particularly poor that only about one third of his force was engaged.


26 April
Two British ironclads, Leo and Sagittarius, transit the Welland canal. They will be employed in wresting control of the upper lakes from the Union, which will prove especially important as there are ships being constructed at Erie (Presque Isle from the last war). They will be joined as soon as possible by Libra, Scorpio and Pisces (now in transit from Britain).
Also on this date, a Confederate probing attack marches down the Rockville Turnpike. They make it through the fort ring (there is dead ground around the turnpike, and Fort Kearny is no more than a construction site) and Meade, now in charge of defending the Capital, deploys much of his reserve to defend Rock Creek.

27 April
Further Confederate forces are marching through the Rockville gap. Meade is ordered to repulse them, as by now some 24-lbers (naval guns taken from Norfolk Naval Yard, forming part of the CSA siege train) are firing into Fort Reno and Fort DeRussey from the less-protected Washington side.
Preparations for the attack will take until the 28th April.
At four in the afternoon of this date, McClellan's army launches an attack towards Confederate communications in the area of Bethesda. Much of the CS army in this area has been drawn off to reinforce the penetration of the DC fort ring, but McClellan has the misfortune to attack while further siege guns are being moved forwards - his troops come under a deadly crossfire from a dozen 32-lbers firing cannister and grape, and the assault bogs down.
McClellan decides to attempt normal approaches (essentially siege operations) in order to get his Parrott guns close enough to neutralize the 32-lbers with counter battery fire.