Contrary to the advice above, whether 1st LT, 2nd LT, LTjg or LT, as the case may be depending on service branch, most will simply go by lieutenant or "LT" would also be fine. Similarly generals and admirals don't usually add their respective prefixes and usually go by just general or admiral, nor do LCDRs or LT Col.s, who usually will just go by commander or colonel.