Four new tuners — including one from “Bloody Bloody Andrew Jackson” composer Michael Friedman and another by “Maple and Vine” scribe Jordan Harrison — will receive developmental staged readings at Eugene O’Neill Theater Center’s National Music Theater Conference.Annual conference at the O’Neill in Waterford, Conn., has helped launch tuners including “Nine,” “Avenue Q” and “In the Heights.” Music-theater program runs concurrently with a similiar O’Neill developmental program for new plays. The quartet of musicals are: n “Unknown Soldier,” with music by Friedman, book by Daniel Goldstein (also a director whose credits include “Godspell”) and lyrics by Friedman and Goldstein. Plot traces the search for a young solider, first by a woman who loves him and then, 80 years later, by the woman’s granddaughter. n “Son of a Gun,” with songs by Don Chaffer of band Waterdeep and book by Chris Cragin and Chaffer. Bluegrass rock tuner follows a man who wants to quit the family band. n “Suprema,” with music by Daniel Zaitchik (“Picnic at Hanging Rock”), lyrics by Harrison and Zaitchik and book by Harrison, whose “Maple and Vine” recently attracted buzz at the Humana Festival of New Plays. Storyline centers on the man who created the lie detector test and Wonder Woman. n “The Shadow Sparrow,” from book writer Anton Dudley, lyricist Charlie Sohne and composer Keith Gordon, about a man and a woman who meet at Pere-LaChaise Cemetery in Paris. Selections were chosen from more than 170 musicals received through the O’Neill’s open submissions process, under artistic director Paulette Haupt. The conference runs June 25-July 15.