Tuesday marked a milestone for the 12-year-old war in Afghanistan, with NATO forces officially handing over responsibility for the country's security to Afghan government forces. Since 2010, when President Barack Obama accelerated training as part of his rapid surge of forces into the country, the Afghan National Army has grown from around 100,000 members to 195,000. But it still faces a number of challenges, including a desertion rate so high that it needs 50,000 new recruits every year to replace those who leave). In December 2012, a Pentagon report determined that only one of the Afghan military's 23 brigades was able to operate effectively without NATO support. Now, Afghan troops will have to do just that; except in rare cases, they will no longer be able to rely on the support of U.S. warplanes, medical evacuation helicopters, or ground troops. Here's a look back at the long preparation for this week's big handover. An Afghan National Army soldier assigned to the Mobile Strike Force Kandak fires an RPG-7 rocket-propelled grenade launcher during a live-fire exercise supervised by Marines Team on Camp Shorabak, Helmand province, Afghanistan on May 20, 2013. U.S. Marine Corps photo by Staff Sgt. Ezekiel R. Kitandwe Personnel from the Afghan National Army, Afghan Local Police, and Afghan National Civil Order Police throw their hats in the air as they celebrate the receipt of the Explosive Hazard Reduction Certificate of Completion, marking the end of their training with the U.S. Army at FOB Warrior in Ghazni province on May 29, 2013. Afghan National Army Special Forces members prepare explosive charges during training on a range in the Washer district of Helmand province on April 20, 2013. U.S. Army photo by Sgt. Benjamin Tuck/Released Soldiers with the Afghan National Civil Order Police smoke cigarettes at sunset during a two-day joint mission with the United States Army's 3rd Battalion, 41st Infantry Regiment near Command Outpost Siah Choyin in Kandahar on March 25, 2013. Photo by Andrew Burton/Getty Images A soldier with the Afghan National Civil Order Police blows a bubble with his gum during a two-day joint mission with the United States Army's 3rd Battalion, 41st Infantry Regiment near Command Outpost Siah Choy on March 26, 2013 in Kandahar province, Afghanistan. Afghan soldiers (L) speak to a local Afghan while a medic in the U.S. Army's 1st Battalion, 36th Infantry Regiment, Charlie Company (R) monitors a soldier who has just survived a blast from an improvised explosive device (IED) while driving a vehicle during a mission near Command Outpost Pa'in Kalay on March 19, 2013 in Kandahar province, Afghanistan. New Afghan National Army soldiers stand in ranks for their graduation from Regional Military Training Center-North in Mazar-e-Sharif on July 5, 2012. Photo by Mass Communication Specialist 2nd Class (SW) Cory Rose A member of Afghan National Army Special Forces goes over targets with Afghan National Army soldiers during live-fire training in Herat province, Afghanistan on Feb. 7, 2013. U.S. Marine Corps Photo by Sgt. Pete Thibodeau An Afghan Security Guard checks out an area before firing rounds into the mountainside with U.S. Army Sgt. Jeremy A. Wortmann, an infantry team leader from St. Louis, in Kunar province, Afghanistan. Photo by U.S. Army Staff Sgt. Mark Burrell, 210th MPAD Gunnery Sgt. Jeremiah Johnson receives updates via radio transmission from the mobile combat operations center about the progress of the Afghan National Army's clearing operation in Trek Nawa, Afghanistan on Feb. 9, 2013. U.S. Marine Corps photo by Sgt. Bobby J. Yarbrough Corpsmen with Combat Logistics Regiment 2, II Marine Logistics Group provide medical care to an Afghan Uniformed Police officer at Combat Outpost Musa Qa'la, Afghanistan, on May 18, 2013. Afghan National Army soldiers participate in a joint patrol with U.S. Army soldiers near Command Outpost Pa'in Kalay on April 6, 2013 in Kandahar province.