The WMAM code calculates spherical harmonic models of the natural magnetisation of the Earth’s crustal geology. In essence, the model allows us to estimate the value of the full magnetic field vector at any location, based on scattered measurements of only the scalar magnetic field. These modelled values of the magnetic field serve many important purposes, such as geological research, navigation, and safe resource extraction. Global spherical harmonic models of degree 1440 (∼28 km resolution) have been successfully computed on the British Geological Survey HPC facility, but such runs require the full BGS compute capacity (512 cores) for up to six days. Further, the resolution of the available scalar field measurements is too high to be fully exploited by the WMAM code, limiting models of the crustal magnetic field to a resolution of 28 km. However, following a successful ARCHER2 eCSE project, we refactored the WMAM code such that it can produce models of spherical harmonic degree 2000 (∼20 km resolution). We ran the code at this resolution using 64 ARCHER2 nodes (8,192 cores) for 3 hrs and 44 mins. The resulting model power spectra and magnetic field maps showed excellent agreement with the BGS1440 model and original data and thus the potential to explore the modelling process and gain new knowledge about crustal magnetic fields.