A .DT1 file contains terrain elevation data used by military GIS software. It has medium granularity between .DT0 and .DT2 files. .DT1 files are binary and can be read by GIS applications. To open a .DT1 file on Windows, right-click it, open with another app, and set to always use that app. On Mac, right-click, open with other app, and set to always open with that app. On Linux, right-click, open with another app, and select an app. If the file does not open in FME Desktop, create a file association in Properties. Update FME Desktop to the latest version. A .DT1 file can be merged into a File Geodatabase Raster Catalog to create a mosaic. .DT1 files have a signature starting with bytes 00 00 80 3F 00 00 00 00. The file format is used in 30% of .DT1 files. These files are 2.9 MB – 12 MB in size. Files contain words like DTED, DSIUOOPUBLIC SALE/NO RESTRICTION, USCNIMA. An example filename is N30.DT1. .DT1 files are classified as GIS Files used on Windows and Mac. These file types have low popularity but detail terrain data. More information on opening these files is below. Be careful as .dt1 files can come from unknown sources. Similar misspellings occur like .ct1 or .ft1. .DT1 file format is used by FME Desktop and other GIS software. Free online .DT1 tools allow viewing, editing, and comparing without installing anything.