Sirs:
If you do a "google" search using the words "longnecker" and "hunley" it should lead you to an article out of Port Lavaca Texas describing several men out of Shea's Batallion Texas Light Artillery (including an uncle-type ancestor of mine) who were involved in the Singer Secret Service. These men also laid mines during the Red River Campaign. The mines were designed by Edgar Collins Singer and Dr. J.R. Fretwell, who were also in the batallion with them.
The Port Lavaca men (several) were also involved in the CSS Hunley Submarine project. Googling "Hunley" and "Port Lavaca" will also find the article.
Last year at the National Archives in DC I found records of these men mentioned who were quickly detailed to General Rain's mine laying operations and then from there, on to Charleston with the Hunley operations. There are some special orders specifically sending E.C. Singer and others to Charleston to work on torpedo operations and he may have been the one who designed the spar torpedo for the boat.
Also, last year there were Civil War letters for sale on E-Bay briefly describing William Longnecker and artillery partner James Jones (from the Texas outfit) laying mines during the Red River campaign. They must have been in the "Secret Service" at that time.
I also found confederate muster cards for the men mentioned in the Calhoun County article on the Texans who helped build and crew the Hunley and the cards relate that they were pulled out of active duty for special duty torpedo work. These muster cards include EC Singer and JR Fretwell, the unit's surgeon.
I would love to hear from you guys who are researching the Singer Secret Service as I too, am trying to find out more because of family involvement. (Most fought for the Union but not all!)
Contact me and I will e-mail you the EBay letter excerpts as an attachment and you can decide for yourselves. We can chat later if you like.