This castable mix will primarily be used in areas where standard brick shapes cannot be used. Type I, 3000 °F conventional castable mix, is used in shock-hardened burner front walls of naval boilers as a replacement for burner tile and adjacent high alumina firebrick and for general furnace repairs. Type II insulating castable mix is used in special applications around naval boiler superheater access doors where a high-temperature insulating castable is necessary. Type III lightweight insulating castable mix is used as a replacement for MIL-B-16008 (ASTM F1312) insulating brick where it is desirable to reduce insulating brick cutting around firebrick anchors. Types II and III insulating castable mix are not intended for direct exposure to furnace gasses. Existing stock of type I conventional castable mix manufactured to MIL-C-717F dated 12 November 1987 is acceptable for use until depleted. These castable mixes have been evaluated and tested for naval service conditions required by MIL-B-18381D that include high shock, rapid light-off and frequent light-off and securing cycles. These conditions are not considerations for all commercial products.