air mobility sales declined by $ 535 million primarily due to c-130j deliveries ( 12 in 2006 compared to 15 in 2005 ) and lower volume on the c-5 program . combat aircraft sales increased by $ 292 million mainly due to higher f-35 and f-22 volume , partially offset by reduced volume on f-16 programs . other aeronautics programs sales increased by $ 83 million primarily due to higher volume in sustainment services activities . operating profit for the segment increased 21% ( 21 % ) in 2007 compared to 2006 . operating profit increases in combat aircraft more than offset decreases in other aeronautics programs and air mobility . combat aircraft operating profit increased $ 326 million mainly due to improved performance on f-22 and f-16 programs . air mobility and other aeronautics programs declined $ 77 million due to lower operating profit in support and sustainment activities . operating profit for the segment increased 20% ( 20 % ) in 2006 compared to 2005 . operating profit increased in both combat aircraft and air mobility . combat aircraft increased $ 114 million , mainly due to higher volume on the f-35 and f-22 programs , and improved performance on f-16 programs . the improvement for the year was also attributable in part to the fact that in 2005 , operating profit included a reduction in earnings on the f-35 program . air mobility operating profit increased $ 84 million , mainly due to improved performance on c-130j sustainment activities in 2006 . backlog decreased in 2007 as compared to 2006 primarily as a result of sales volume on the f-35 program . this decrease was offset partially by increased orders on the f-22 and c-130j programs . electronic systems electronic systems 2019 operating results included the following : ( in millions ) 2007 2006 2005 .
what was the percentage change in backlog from 2006 to 2007?
net sales for electronic systems increased by 6% ( 6 % ) in 2007 compared to 2006 . sales increased in missiles & fire control ( m&fc ) , maritime systems & sensors ( ms2 ) , and platform , training & energy ( pt&e ) . m&fc sales increased $ 258 million mainly due to higher volume in fire control systems and air defense programs , which more than offset declines in tactical missile programs . ms2 sales grew $ 254 million due to volume increases in undersea and radar systems activities that were offset partially by decreases in surface systems activities . pt&e sales increased $ 113 million , primarily due to higher volume in platform integration activities , which more than offset declines in distribution technology activities . net sales for electronic systems increased by 7% ( 7 % ) in 2006 compared to 2005 . higher volume in platform integration activities led to increased sales of $ 329 million at pt&e . ms2 sales increased $ 267 million primarily due to surface systems activities . air defense programs contributed to increased sales of $ 118 million at m&fc . operating profit for the segment increased by 12% ( 12 % ) in 2007 compared to 2006 , representing an increase in all three lines of business during the year . operating profit increased $ 70 million at pt&e primarily due to higher volume and improved performance on platform integration activities . ms2 operating profit increased $ 32 million due to higher volume on undersea and tactical systems activities that more than offset lower volume on surface systems activities . at m&fc , operating profit increased $ 32 million due to higher volume in fire control systems and improved performance in tactical missile programs , which partially were offset by performance on certain international air defense programs in 2006 . operating profit for the segment increased by 17% ( 17 % ) in 2006 compared to 2005 . operating profit increased by $ 74 million at ms2 mainly due to higher volume on surface systems and undersea programs . pt&e operating profit increased $ 61 million mainly due to improved performance on distribution technology activities . higher volume on air defense programs contributed to a $ 52 million increase in operating profit at m&fc . the increase in backlog during 2007 over 2006 resulted primarily from increased orders for certain tactical missile programs and fire control systems at m&fc and platform integration programs at pt&e. .