Communication systems can have different strengths and weaknesses. By combining different types of radio systems in a heterogeneous network, the user needs may be better served. Mobile ad hoc networks (MANET) are used to overcome specific challenges of military communications, for example long ranges and low dependence on fixed infra-structure. A tactical MANET with many nodes and high mobility is typically narrowband and thus has low data capacity. We describe how a narrowband MANET can be part of a heterogeneous network from a routing point of view. Protocols for routing supporting heterogeneous networks have been developed by the Internet Engineering task Force (IETF). However, even with protocol versions adapted for MANETs, the routing overhead cost can be high in networks with a large number of nodes and high mobility. In order to estimate the routing overhead cost, we need to know how often there are changes in theMANET of the type that cause a routing protocol to update the topology information through the heterogeneous network. We present three different concepts of including a MANET in a heterogeneous network. For these concepts, different type of network changes cause topology information updates. We evaluate two of the concepts and estimate how often these types of events occur, using a tactical scenario with real terrain. There are considerably fewer events causing updates when using the concept with separate MANET and internet routing, as compared to using only internet routing. The difference is of the order of several magnitudes.