North American P-51D Mustang

Model History:

The P-51 Mustang is arguably the best fighter of World War II.  The P-51D, with its Packard built Rolls Royce Merlin engine is certainly the most iconic fighter of World War II.  It was armed with six fifty caliber machine guns and could carry bombs, rockets, or fuel tanks under the wings.

History of Sierra Sue II:

Sierra Sue II is a P-51D-20-NA Mustang fighter manufactured at North American’s Inglewood plant in southern California as ship number 516, construction number 122-31401.  Upon acceptance by the Army Air Force, she was assigned serial number 44-63675.

Sierra Sue II is most notable today for several reasons:

  • Even though there are over one hundred mustangs flying today, Sierra Sue II is one of a handful of mustangs that actually saw combat in World War II.
  • Sierra Sue II has a rich history in Minnesota having been based here since 1979.  Her longtime owner Roger “Doc” Christgau was an outstanding pilot and doctor and was well known on the local airshow circuit.  You could often find Doc out with his airplane on Saturday mornings at Flying Cloud Airport at the old Planes of Fame East Air Museum.
  • When Sierra Sue II was restored by AirCorps Aviation, the goal was to make the plane as close as possible to how it appeared when it was delivered from the factory.  It includes working World War II era radios and full armor plating among other authentic details.

Military History

25 November 1944 44-63675 is accepted by the Army Air Force.
27 November 1944 44-63675 is delivered to the Army Air Force.
29 January 1945 44-63675 is shipped overseas to Belgium.
1st week of April 1945 44-36675 is assigned to 402nd Fighter Squadron, 370th Fighter Group, 9th Air Force (Code E6-D) and 1st Lt. Robert (Bob) Bohna.  Bohna names the plane Sierra Sue II after a girl in his high school.
1st half of 1947 Sierra Sue II is purchased in one of the last lots of P-51’s by the Swedish Government and assigned the Swedish Air Force number Fv26152 and re-designated J26.
June 1948 Sierra Sue II arrives at her new station F4 near Ostersund, Sweden.  She is assigned to the third squadron (colored yellow) and gains the nickname of “Gul Kalle” which translated means yellow K (a yellow K is painted on the vertical tail).  She is assigned to pilot Sten Soderquist who flies her for the next four years.
October 1952 Gul Kalle is transferred to F8 near Stockholm for use as a staff plane.  Redesignated “Gron Kalle” which means green K (yellow k is repainted green).  She also has the name “Kleopatra” painted on the nose.
18 September 1954 Gron Kalle/Kleopatra is sold, disassembled, and shipped via the port of Malmo, Sweden to Nicaragua to serve in the Nicaraguan Air Force.  Once in Nicaragua, she is reassembled and put into service at Las Mercedes Air Base near Managua as GN91.
By 1961 GN91 is retired from service and eventually put on outdoor display at Las Mercedes.

Civilian History

30 July 1971 GN91 is purchased from the Nicaraguan Air Force by Dave Allender of San Mateo, California and registered as N5452V and Race number 19.  Allender makes numerous modifications to the airplane and paints it bright red.
8 March 1977

Race 19 is sold to Roger “Doc” Christgau of Austin, MN.  For a video about Doc’s life, check out this video from AirCorps.

1977-1983 Aircraft restored to a stock Mustang configuration by Jack Cochrane in Hollister, California.
30 October 1979 FAA registration changed to N1751D.
May 1983  Sierra Sue II departs Hollister, California for its new home in MN.  Airplane is eventually repainted as Sierra Sue II in a semblance of her World War II markings on the left side of the fuselage.  The right side of the fuselage is painted to partially resemble her Swedish markings as Gul Kalle.  Roger owns the airplane for more than 30 years and is a fixture at airshows during the ’80’s and ’90’s.
1 July 2011 Sold to Paul Ehlen of Hamilton, Montana.  Ehlen ships the airplane to AirCorps Aviation in Bemidji, MN for a complete restoration to factory specifications.
17 September 2014

Sierra Sue II’s first flight after a complete restoration by AirCorps Aviation in Bemidji, MN. Coverage of the restoration can be found here.


May 2015 Sierra Sue II joins the Wings of the North collection as the cornerstone of its new museum.
26 July 2015 Paul Ehlen is awarded Reserve Grand Champion for Sierra Sue II at EAA’s AirVenture.  AirCorps Aviation is awarded the Gold Wrench for their work on the restoration of Sierra Sue II.

John Christgau (Doc’s brother) put together a wonderful history of Sierra Sue II while it was still owned by Doc.  It can be purchased from Amazon here. We have copies of this book in the museum gift shop for $15.00

There is also a book by Chuck Cravens titled “Combat Vet P-51 Mustang – The History of Sierra Sue II, World War II Survivor” which documents Sierra Sue’s restoration by AirCorps Aviation.

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