Lance Cpl. Noah Koehl, administration clerk with the 24th Marine Expeditionary Unit, clears his M50 Joint Service General Purpose Gas Mask during annual chemical, biological, radiological and nuclear defense training at the Marine Corps Base Gas Chamber on Camp Lejeune, N.C. Feb. 3. Marines with the 24th MEU trained on the new M50 JSGPM, M50 Joint Service General Purpose Gas Masks, which has been phasing out the 1980s-era M40 Field Protective Mask across the Marine Corps since September 2009. - Lance Cpl. Noah Koehl, administration clerk with the 24th Marine Expeditionary Unit, clears his M50 Joint Service General Purpose Gas Mask during annual chemical, biological, radiological and nuclear defense training at the Marine Corps Base Gas Chamber on Camp Lejeune, N.C. Feb. 3. Marines with the 24th MEU trained on the new M50 JSGPM, M50 Joint Service General Purpose Gas Masks, which has been phasing out the 1980s-era M40 Field Protective Mask across the Marine Corps since September 2009.