ST. LOUIS - Boeing Co. is buying aircraft design and development company Insitu Inc. for undisclosed terms to help boost its presence in the unmanned systems market.

The purchase is expected to close by the end of September, following regulatory approval.

Boeing said Tuesday the purchase does not affect its outlook and said Insitu will operate as a separate subsidiary.

Insitu is based in Bingen, Wash. The company designs, develops and manufactures unmanned air systems, or aircraft that operates without a pilot, for commercial and military applications.

Shares of Boeing rose 41 cents to $68.65 in midday trading.