global horizontal sounding technique
...that on September 29, 1968 a global horizontal sounding technique superpressure balloon became the first balloon to fly for a full year?
...that on <a href="./September_29" id="mwCeQ" rel="mw:WikiLink" title="September 29">September 29</a>, <a href="./1968" id="mwCeU" rel="mw:WikiLink" title="1968">1968</a> a <b id="mwCeY"><a href="./Global_horizontal_sounding_technique" id="mwCec" rel="mw:WikiLink" title="Global horizontal sounding technique">global horizontal sounding technique</a></b> <a href="./Superpressure_balloon" id="mwCeg" rel="mw:WikiLink" title="Superpressure balloon">superpressure balloon</a> became the first balloon to fly for a full year?