We only have the description given by McClellan in letters to Ordnance Dept. officials to go by, but recent copies of these heretofore unknown letters have been found, and they provide MUCH more information than previously known about these first prototype models.
The tree took some time, and several attempts, to get to where it was thought it was acceptable. There were different suggestions regarding stirrups and tree covering, to TWO prototype models were fabricated. One had a bare wood tree ( suggested by Capt. Delos Bennett Sackett, 1st Dragoon Regt.), while the other had a smooth leather cover at the request of McClellan.
Things that were included with the horse equipment sets – saddlebags, shelter tents ( the first shelter halves ? ), halters, bridles, curb bits, snaffle bits, saddles, stirrups, girths. Things that were specifically NOT included: cruppers, breast straps, shoe pouches, saddle holsters, carbine loops.
McClellan made very effusive praise for the work of Lacey & Phillips, and the extreme assistance given by Mr. Samuel R. Phillips in particular – one of the principles of the firm. If McClellan’s statements are take at face value, it appears that much of the final form and function of the resulting equipment was in great part due to their enthusiasm and attention to the task. In multiple communications to the Ordnance Dept., McClellan made it quite clear that he was heartily recommending Lacey & Phillips as the primary supplier of the ‘trial saddles’, if the models were approved. Indeed, he promoted the idea of having Mr. Phillips come to the War Dept. himself and work with the coordinating officer there ( Capt. W.T. Maynadier ) in making necessary changes or alterations that might have been deemed necessary.
What notes that have been found show that both Craig and Davis examined the prototypes, and Davis in particular made some specific recommendations for alterations, as well as confirming some of McClellan’s choices ( leaving off the crupper and breast strap). The changes by Davis help (by inference) to show other details about the models, not mentioned in McClellan’s letters – that the stirrups were equipped with hoods and sweat leathers. Davis recommended that the hoods and sweats be removed, as well as a ‘seat cover’ made of leather – the first real ‘skeleton’ saddle form used by US military forces. It seems that the bare tree recommended by Capt. Sackett was demurred, with the favor going to McClellan’s whip-stitched leather cover, as used on the M1857 trial saddles. [ as an aside, this cover may not have been the preferred type, but Lacey & Phillips only had about five weeks from start to finish, and made a number of different patterns of the tree to get to the one they liked. The time needed to have a rawhide or more formally seamed leather cover may not have been available, especially for a ‘model’ specimen.]
This revised pattern piece was approved by the Secretary, with the initial order of over 300 ‘new McClellan’s pattern horse equipments’ being ordered in mid-February, 1857. It’s not known if the initial pattern pieces were returned to Lacey & Phillips or kept at the War Department, but they disappeared long ago, perhaps recycled into the new 1857 saddles quickly issued in that year.
 McClellan letter to Capt. William T. Maynadier, 23 Dec 1856. Library of Congress. Manuscript Division. George Brinton McClellan Papers: Correspondence II, 1823-1898 mss31898, box B3; reel 45.
 McClellan letter to Colonel Henry Knox Craig, 25 Dec 1856. Library of Congress. Manuscript Division. George Brinton McClellan Papers: Correspondence II, 1823-1898 mss31898, box B3; reel 45.