The YouTube video that shows the Legged Squad Support System (LS3), also informally called AlphaDog, in action is entitled "DARPA Legged Squad Support System (LS3) Demonstrates New Capabilities".
It is shown above in the YouTube video (http://www.youtube.com/watch?v=40gECrmuCaU).
The caption for the YouTube video states: "This video depicts field testing of the DARPA Legged Squad Support System (LS3). The goal of the LS3 program is to demonstrate that a legged robot can unburden dismounted squad members by carrying their gear, autonomously following them through rugged terrain, and interpreting verbal and visual commands."
To learn more about LS3, please visit http://go.usa.gov/rwQB. The LS3 was developed by Boston Dynamics. Its website states, "Boston Dynamics builds advanced robots with remarkable behavior: mobility, agility, dexterity and speed. We use sensor-based controls and computation to unlock the capabilities of complex mechanisms."
And, "Our world-class development teams take projects from initial concept to proof-of-principle prototyping to build-test-build engineering, to field testing and low-rate production."
The DARPA article states, "Today’s dismounted warfighter can be saddled with more than 100 pounds of gear, resulting in physical strain, fatigue and degraded performance. Reducing the load on dismounted warfighters has become a major point of emphasis for defense research and development, because the increasing weight of individual equipment has a negative impact on warfighter readiness."
And, "The Army has identified physical overburden as one of its top five science and technology challenges. To help alleviate physical weight on troops, DARPA is developing a four-legged robot, the Legged Squad Support System (LS3), to integrate with a squad of Marines or Soldiers."