The first true DPICM was the 155 mm M483, produced in the 1970s. By 1975, an improved version, the M483A1, was being used. The projectile carried 88 M42/M46 grenade-like dual purpose submunitions. The 155 mm M864 projectile entered production in 1987, and featured a base bleed that enhances the range of the projectile, although it still carries the same M42/M46 grenades. The base bleed mechanism reduces the submunition count to 72. Work was budgeted in 2003 to retrofit the M42/M46 grenades with self-destruct fuses to reduce the problem of "dud" submunitions that do not initially explode but may explode thereafter upon handling. In Vietnam they were known as "firecracker rounds" owing to the rippling detonation of sub-munitions over a couple of seconds.