As orderly as the soldiers therein, military records seem ideally suited for online research. Though military documents can be found in many of the databases in this year's 101 list, sites in this section are especially useful for finding your ancestors' service records and exploring the wars they fought.
American Battle Monuments Commission
Search for almost 125,000 US war dead buried in 24 overseas cemeteries, as well as more than 94,000 military commemorated on Tablets of the Missing.
Civil War Soldiers & Sailors System
Start your search for Union or Confederate Civil War ancestors in this database of 6.3 million soldier names from 44 states and territories. Soldiers' names link to histories of their regiments and the battles they fought.
Zoom in on an interactive map linked to primers on 341 battles, study timelines and 5,470 photos, and even sing along with Civil War ditties. This is also one of few sites—another being eHistory, below—where you can search the full text of the Official Record ("OR"), which has detailed reports by those who led the charge.
Though not limited to military history, the 130,000 pages here are especially rich in records of conflicts—including the OR, 800 battle overviews, Miller's Photographic History of the Civil War, maps and timelines.
Library of Virginia
Besides being a must for researchers with Virginia kin, this site's digitized resources include an index to soldiers mentioned in nearly 30 years of Confederate Veteran magazine. Military buffs also can tap the Virginia Military Dead Database of 34,402 names, the fully searchable Index to War of 1812 Pay Rolls and Muster Rolls, a database of the commonwealth's Mexican War Soldiers, Index to Virginia Confederate Rosters, an index to Virginians in the Confederate Navy, and 250,000 Virginia WWII Separation Notices.
Louisiana State Archives
The Confederate Pension Applications Index covers more than 49,000 names included in Louisiana state pension applications—a tad easier than scrolling the original 152 rolls of microfilm.
National Park Service Civil War Homepage
Get a jump on your Civil War research with this new site. The war's sesquicentennial commemoration (2011 to 2015) has already begun, and here you can learn about the war's beginnings in "Bloody Kansas."
Nationwide Gravesite Locator
This domestic counterpart to the American Battle Monuments Commission searches the burial locations of veterans and their dependents in Department of Veterans Affairs National Cemeteries, state veterans cemeteries, and other Department of Interior and military cemeteries.
New York State Civil War Soldier Database
More than 360,000 New Yorkers, including three regiments of "Colored Troops," fought in the Civil War. If you suspect your ancestor was among them, check this database.
Pennsylvania State Archives
Pennsylvania's online archives are unusually rich in military history, with 1.5 million records of conflicts from the American Revolution to World War I.
Texas State Library & Archives Commission
Find soldiers from the Lone Star State in the online index of 54,634 Confederate pension applications and Texas Adjutant General Service Records (1836 to 1935).