ARMF-I and ARMF-II were near identical pool reactors. ARMF-I and ARMF-II were housed in a 40-foot by 60-foot cinder block building located just east of the MTR canal tunnel; the building was designed from the initial concept for two reactors. These facilities were swimming-pool-type reactors having light-water moderated cores made up of plate-type fuel elements containing high enriched uranium at 93% U-235. The facilities were located at the National Reactor Testing Station near the Materials Testing Reactor (MTR). Being located near the MTR permitted measurements on short-lived fission products and transmuted isotopes. By use of the capsule 'transfer tube' connecting the MTR and ARMF canals, a capsule could be transferred from the MTR hydraulic rabbit to the ARMF and prepared for reactivity measurements in 15 minutes.