question: When was the catastrophic EF5-rated multiple-vortex tornado struck after which the Missouri Militia members have been active in disaster relief?
answer: May 22, 2011
context: Title: 2011 Tuscaloosa–Birmingham tornado
  Passage: The 2011 Tuscaloosa–Birmingham tornado was a large and violent EF4 multiple-vortex tornado that devastated portions of Tuscaloosa and Birmingham, Alabama, as well as smaller communities and rural areas between the two cities, during the late afternoon and early evening of Wednesday, April 27, 2011.  It is one of the costliest tornadoes on record.  It was one of the 362 tornadoes in the 2011 Super Outbreak, the largest tornado outbreak in United States history.  The tornado reached a maximum path width of 1.5 mi during its track through Tuscaloosa, and once again when it crossed Interstate 65 north of Birmingham, and attained estimated winds of 190 mph shortly after passing through the city.  It then went on to impact parts of Birmingham as a high-end EF4 before dissipating.  This was the third tornado to strike the city of Tuscaloosa in the past decade, and the second in two weeks.
  Title: 1948 Tinker Air Force Base tornadoes
  Passage: The 1948 Tinker Air Force Base tornadoes were two tornadoes which struck Tinker Air Force Base in Oklahoma City, Oklahoma, on March 20 and 25, 1948.  Both are estimated to have been equivalent to F3 in intensity on the modern Fujita scale of tornado intensity, which was not devised until 1971.  The March 20 tornado was the costliest tornado in Oklahoma history at the time.  On March 25, meteorologists at the base noticed the extreme similarity between the weather conditions of that day and March 20, and later in the day issued a "tornado forecast", which was verified when a tornado struck the base that evening.  This was the first official tornado forecast, as well as the first successful tornado forecast, in recorded history.
  Title: 2011 Joplin tornado
  Passage: The 2011 Joplin tornado was a catastrophic EF5-rated multiple-vortex tornado that struck Joplin, Missouri, late in the afternoon of Sunday, May 22, 2011.  It was part of a larger late-May tornado outbreak and reached a maximum width of nearly 1 mi during its path through the southern part of the city.  It rapidly intensified and tracked eastward across the city, and then continued eastward across Interstate 44 into rural portions of Jasper County and Newton County.  It was the third tornado to strike Joplin since May 1971.
  Title: Missouri Militia
  Passage: The Missouri Militia is a private, non-profit civilian defense organization in the U.S. state of Missouri.  The Missouri Militia is not a part of the Missouri Reserve Force.  which is the state defense force for the state of Missouri.  Its members have been active in disaster relief after the 2011 Joplin tornado.
  Title: Multiple-vortex tornado
  Passage: A multiple-vortex tornado is a tornado that contains several vortices (called subvortices or suction vortices) rotating around, "inside" of, and as part of the main vortex.  The only times multiple vortices may be visible are when the tornado is first forming or when condensation and debris is balanced enough so that subvortices are apparent without being obscured.  They can add over 100 mph to the ground-relative wind in a tornado circulation, and are responsible for most (if not all) cases where narrow arcs of extreme destruction lie right next to weak damage within tornado paths.
citations: Missouri Militia 2011 Joplin tornado