We investigate how individual workers and local labour markets adjust over a long time period to a discrete and plausibly exogenous technological shock, namely the introduction of containerization in the UK port industry. This technology, which was introduced rapidly between the mid‐1960s and the late‐1970s, had dramatic consequences for specific occupations within the port industry. Using longitudinal micro‐census data, we follow dockworkers over a 40‐year period and examine the long‐run consequences of containerization for patterns of employment, migration and mortality. The results show that the job guarantees negotiated by the unions protected dockworkers' employment until the guarantees were removed in 1989. A matched comparison of workers in comparable unskilled occupations reveals that, even after job guarantees were removed, dockworkers did not fare worse than the comparison group in terms of their labour market outcomes. Our results suggest that job guarantees provided a safety net which reduced the cost to workers of sudden technological change.