alternatehistory.com

9 June

Dahlgren is still attempting various trials with his 11" gun and the modifications and improvements thereof, to attempt to find a way of reliably penetrating the side of a British ironclad.
On encouragement from a local inventor, he has attempted the use of guncotton - from a batch produced with great difficulty and which resulted in several small accidental explosions - on the grounds that it has been observed that unburned powder exits the barrel of the Dahlgren gun when it is fired. The faster burning guncotton is supposed to alleviate this.
In the event, the result is not encouraging. The faster burning powder produces pressure at the breech much faster than gunpowder, and the metallurgy of the 11" gun is simply not up to it - Dahlgren is lucky to escape injury as high velocity fragments go everywhere.

Dahlgren writes up his conclusions - which are, essentially, that the 11" gun as it exists is not capable of regularly withstanding an explosion of the power required to launch a projectile through the sides of a British ironclad (at least in anything more than the most marginal way). He also enquires as to where better iron could be obtained - since he feels part of the fault is with the gun metal - and is told that the best quality of iron used at Springfield was mainly sourced from England pre-war. (They are currently 'improvising', which has led to a noticeable decline both in numbers and quality of Springfield rifles.)

A curiosity about the result is that, as the tests are being done in Pennsylvania in June, they are giving a rosier picture for the armour than an identical test in Febuary would. This is due to the transition temperature of iron, a subject not well understood at this time.

McClellan hears about the tests, and they are the source of a letter complaining about how many guns Dahlgren is destroying in his tests while the Army of the Potomac goes under-armed. This prompts a rather acerbic exchange of letters.


The weather becomes stormy towards the afternoon, and by nightfall at New York there is 10/10 cloud with the occasional squall of rain.
Under cover of night, the Vanderbilt slips out of New York harbour. She is using mainly her sails, with her paddles used primarily for steerage (with the best clean Pennsylvania coal to reduce the smoke and flame she produces) and manages to evade detection.
Armed with several naval guns, she is to be a commerce raider in an attempt to pressure the British into giving up on the war (having been given to the US Navy months earlier by her former owner). The main thing to recommend her as a commerce raider is her extreme speed (fourteen knots dash, faster than the Mersey and the Orlando - themselves extremely fast British frigates), though some in the US Navy called for her to be made a blockade runner instead. (The US is not well provided with very fast ships, and obtaining them from the Clyde or other British shipbuilders is obviously not possible.)