The use of numerical simulations to design and analyze new products requires both conceptual and operational knowledge. This paper describes COMPANION: an intelligent multimedia system for vocational training used by engineers and technicians. A key concept in terms of training methodology is that of "situated learning," or continuous learning in the workplace. Cognitive apprenticeship is a design model supporting situational learning which is an extension of the traditional apprenticeship model focusing on learning problem solving skills in the practice of performing authentic tasks. The novice (apprentice) watches the expert performing the task, and the expert allows the novice to ask questions and perform small parts of the task, with the amount of the task carried out by the novice increasing as experience is gained. Following an introduction in section one, section two describes the different student uses of COMPANION, and shows how cognitive apprenticeship and hypermedia are integrated in the whole system. Section three focuses on the structure of COMPANION. Section four details the content of hypermedia modules used in conceptual knowledge acquisition. Section five describes how the operational knowledge is structured and acquired. Sections six and seven, respectively, detail the engineering activity and the technical assistant, which embodies the knowledge that becomes operational during problem solving with collaboration between the student and COMPANION. (Contains 17 references.) (Author/MAS)