Fire Zone Purge
Two bullet points, one conditional and one not. First: if a friendly MILITARUM TEMPESTUS OFFICER model is your WARLORD, friendly TEMPESTUS SCIONS units have BATTLELINE and +1 OC. That is a real list-building commitment, because it costs you the chance to make Lord Solar Leontus or a Castellan your Warlord, and in exchange your Scions stop being a raiding party and start being troops that can hold ground. Second, and with no Warlord condition attached: when a friendly MILITARUM TEMPESTUS unit is selected to shoot, if that unit was set up this turn, that unit's ranged attacks have +1 to hit rolls. Be precise about the trigger, because it is usually described as a bonus for arriving from Reserves. It is not. It says set up this turn, which covers a Deep Strike arrival but also covers a unit set up by any other means, and Faction Pack v1.2 adds Deep Strike to the Tempestus Scions datasheet itself. This detachment carries no UNIQUE banner in the pack, states no tag in its rule text, and is listed with no tag in the Munitorum Field Manual or Wahapedia, which makes it the most flexible 1 DP splash in the faction: it pairs with all seven 2 DP detachments and with both other 1 DP detachments.