We study the development of a duopoly in a continuous-time model of capacity investment under no commitment by firms regarding future actions. While capacity units are costly, indivisible, durable, and large relative to market size, early entry cannot secure a first-mover advantage and both firms are active beyond some level of market development. We evaluate the investment real options in that context. In the early industry development phase, the sole Markov Perfect Equilibrium (MPE) is a preemption equilibrium with the first industry investment occurring earlier (hence being riskier) than socially optimal. Once both firms hold capacity, tacit collusion, taking the form of postponed capacity investment, may occur as a MPE. Volatility and the expected speed of market development play a crucial role in competitive behavior: we show that the emergence of tacit collusion equilibria is favored by higher demand volatility, faster market growth, as well as by lower discount rate.