In 1870, she signed on as a scout, and adopted the uniform of a soldier. It is unclear whether she was actually enlisted in the U.S. Army at the time. From then on she mostly lost touch with her younger siblings, preferring to live a more wild and unsettled life. Calamity Jane, as she would become known, did live a very colorful and eventful life starting in 1870, but as historians have since discovered, she was prone to exaggerations about her exploits, and, at times, outright lies.
She would often claim association or friendship with notable famous Old West figures, almost always making these claims after their death. Years after the death of General George Armstrong Custer, she claimed that she served under him from her initial enlistment, at Fort Russell, and that she served under him during the Indian Campaigns in Arizona. However, no records exist to show that Custer was ever assigned at Fort Russell, and he did not take an active part in the Arizona Indian Campaigns, but rather was tasked with handling the Plains Indians. It is more likely that she served under General George Crook, who was stationed at Fort Fetterman, Wyoming. This would be the first of many false claims made by her.
She did serve in one campaign in which General Custer was involved, following the spring of 1872. Generals Custer, Miles, Terry and Crook were dispatched with their forces to handle Indian uprisings near present day Sheridan, Wyoming, which would be called the "Muscle Shell Indian Outbreak", and is also referred to as the "Nursey Pursey Indian Outbreak". This is the only confirmed opportunity she had to meet Custer, although it is unlikely that she did.
Following that campaign, in 1874, her detachment was ordered to Fort Custer, where they would remain until the following spring. During this and other campaigns involving Custer and Crook together she was never attached to Custer's command.
She was involved with a number of campaigns in the long-running military conflicts with Native Americans. One story, told by her, has her acquiring the nickname "Calamity Jane" in 1872 by rescuing her superior, Captain Egan, from an ambush near Sheridan, Wyoming, in an area known then as Goose Creek, Wyoming. However, even back then not everyone accepted her version, and in another story it's said that she acquired it as a result of her warnings to men that to offend her was to "court calamity". Calamity Jane accompanied the Newton-Jenney Party into the Black Hills in 1875, along with California Joe and Valentine McGillycuddy.
One verified story about her is that in 1875 her detachment was ordered to the Big Horn River, under General Crook. Bearing important dispatches, she swam the Platte River, and traveled 90 miles at top speed while wet and cold to deliver them. Due to this action, she became quite ill. After recuperating for a few weeks, she rode to Fort Laramie, Wyoming, and later, in July of 1876, she joined a wagon train headed north, which is where she first met Bill Hickok, contrary to her later claims.