What is the test for a charge of possession of a deadly or dangerous weapon?

"An indictment is required to set forth the elements of the offense sought to be charged." United States v. Debrow, 346 U.S. 374, 376, 74 S.Ct. 113, 114, 98 L.Ed. 92 (1953); see also United States v. Krasovich, 819 F.2d 253, 255 (9th Cir.1987) (same). Here, there is no dispute that the indictment did not allege the use of a deadly or dangerous weapon. Rather, the question is whether the use of such a weapon is an essential element of the crime, or whether it is simply a "sentence enhancement" which need not be pled in the charging indictment.