strategic materials
Refers to materials essential for national defense or economic security, often subject to export controls or stockpiling.
The government is strengthening its stockpile of strategic materials.
Rare earths are regarded as important strategic materials.
戦略物資 is a near-synonym, but 物資 often implies goods or supplies in a broader logistical sense, while 物質 emphasizes the material or substance itself.
Compound of 戦略 (strategy) and 物質 (material, substance).