A conceptual definition of combat effectiveness is the overall capability of a force to produce a desired outcome from combat against an enemy force. An ability to measure combat effectiveness is critical to strategic and tactical decision making; however, it is a challenging task to develop an operational metric for combat effectiveness due to the large complexity presented by the rich context of a combat environment. The present paper contends that, under a direct fire engagement, combat effectiveness can be reasonably assessed by the prevalence of attack opportunities a given force creates in a combat environment. The paper proposes a method to quantitatively measure combat effectiveness of a military force in a direct fire engagement environment. The proposed metric is based on a meta-network representation that captures various aspects of a combat environment. Using a meta-network representation, two types of basic unit structures of attack opportunity - isolated and networked - are identified, which are then used as a basic element for measuring combat effectiveness. Prevalence of network motifs in a networked combat environment and availability of attack opportunities are computed as a measure of a military force's combat effectiveness.