Many large and highly complex engineering projects present enormous technical and financial risks to organizations. This is especially true in the defence industry where budgets can potentially run into billions and the project lifecycle may extend over many years. In frequent cases, such projects are too much for a single organization to undertake. One option that is becoming ubiquitous across contemporary defence projects is to spread the risk by forming an alliance between several organizations. Unfortunately, forming an alliance between potentially competing organizations brings its own set of challenges and risks. The operating conditions of the business environment are characterized by frequent changes in products, services, processes, organizations, markets, supply and distribution networks. The partners need to work together as an entity to achieve a goal but the relationships within the alliance are often disrupted by the established practices, culture and motivation of the individual companies. This paper starts by examining how risks can essentially multiply when an alliance is formed and what potential impacts these risks have on project success. A novel 3PE method for modeling the structure of an alliance with the three elements being product, people, process, and their interactions is proposed within an alliance environment. This methodology is then used to calculate the increase in interactions between the 3Ps with the introduction of more organizations to the alliance. By examining each of the elements and their interactions, risks are identified, and the key drivers are exposed. Finally, a case study is presented that illustrates how the architectural model can be used to estimate the probability of failure of the alliance.