The Navajo code was formally developed and modeled on the Joint Army/Navy Phonetic Alphabet that uses agreed-upon English words to represent letters. Since it was determined that phonetically spelling out all military terms letter by letter into words while in combat would be too time-consuming, some terms, concepts, tactics, and instruments of modern warfare were given uniquely formal descriptive nomenclatures in Navajo. For example, the word for shark referred to a destroyer, while silver oak leaf indicated the rank of lieutenant colonel.[39]