The nation's critical infrastructure, information systems, and telecommunication networks are vulnerable and threatened by an ever-growing number of attacks in cyberspace. An essential element of the nation's comprehensive approach to cybersecurity is the ability for the Department of Defense to protect and defend its information enterprise. Unfortunately, decision-making uncertainty experienced by military leaders when determining the appropriate response to a cyber attack can impede cybersecurity efforts. This qualitative, phenomenological study was used to explore the perceptions and lived experiences of 21 senior military officers serving in cyber warfare divisions for the Chairman of the Joint Chiefs of Staff in Washington, DC. The synthesis of 10 key themes that were exposed during the phenomenological reduction analysis indicated that the decision-making uncertainty experienced by the participants following a cyber attack was described by five interdependent characteristics: (a) response process, (b) human factors, (c) governance, (d) technology, and (e) environment. These interrelated characteristics are similar to the factors found in the literature that describe organizational change uncertainty. The study further indicated the response decision-making process used by senior military officers following a cyber attack was best described by poliheuristic, noncompensatory decision theory. Recommendations for leadership were centered on policy and strategic changes, improving senior officer experience and situational awareness, and enhancing collaboration and coordination among the U.S. government departments and agencies. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]