3 pages, 4 3/4 x 8 in., creased throughout, with some small separations to creases, spotting/staining thoughout. On U.S. Christian Commission letterhead.  

Castle writes to his father, mother, and sister about the recent goings on in the capital city, in part: "We have left the State of Virginia and am after old Lee know wich [sic] are within about 3 miles of washington we left Pertsburg [sic] in the 10 of July and arived [sic] in wishington [sic] on the 12 the Rebbles [sic] has don [sic] a good deal of damige [sic] before we got here but I think they had beter git [sic] out of here know [sic] don't you fore [sic] if thay [sic] don't thay will git [sic] a good licken [sic] fore we are the boys that can give it to them wen [sic] we got here thay had got all the invalid Corps and citisins [sic] out of washington got them in line to protect the city but the Johnys [sic] Drove them but wen our Corps came up they fell back our corps is all that left Pertsburg and I think we will have a hard fite [sic] here but let her com tha [sic] boys is all redy [sic] fore it..." 

Castle then writes that while he hopes to meet his family again on earth, he will try to live in order to meet them in Heaven if he should fall in battle. Records show that Castle was shot and killed later that day. At the bottom of the letter, in a different hand, "Dick's last letter" is written and underlined.

The Battle of Fort Stevens began on 11 July when Confederate Major General Jubal A. Early's skirmishers tested the fortifications encircling Washington, DC, manned by clerks and convalescent troops. Veteran reinforcements arrived overnight to help protect the city, and on 12 July, Union forces repulsed Early's demonstration against Fort Stevens just north of DC. In the afternoon, a Federal counterattack drove back Confederate skirmishers, and that night Early withdrew from the area. President Abraham Lincoln watched the action and actually came under enemy fire at one point.

Castle was one of an estimated 374 Union casualties of the battle, and though his letter was likely delivered to his parents, it would be his last.